High Phase Angle Research Articles

The effect of phase angle on crack growth mechanisms under thermo-mechanical fatigue loading

The current paper describes TMF crack growth behaviour in an advanced nickel-based superalloy. Changes in behaviour are examined which occur as a function of the phase angle between applied stress and temperature. The fractography of the failed specimens reveals changes from transgranular to intergranular growth between high and low phase angle tests as a result of the onset of high temperature damage mechanisms. More targeted testing has also been undertaken to isolate the contributions of these mechanisms, with specific transitions in behaviour becoming clear in 90° diamond cycles, where dynamic crack growth and oxidation strongly interact.

Dependence of Light Curves on Phase Angle and Asteroid Shape

Abstract We investigate the phase angle dependence of asteroid light curves using numerical scattering models applied to simple body shapes. For simplicity, the Kaasalainen scattering parameters are obtained from the corresponding Hapke scattering laws for C-type, S-type, and V-type asteroids. The spectral types differ substantially in the role of multiple scattering (which is largely a function of their geometric albedos) but we find that the differences on the light curve versus phase relations are modest. Using a Kaasalainen scattering law, the amplitudes and axis ratios with respect to different phase angles from 0° to 140° are plotted for these types of asteroids based on a biaxial ellipsoid shape model. Additionally, we examine the relationship between amplitude and the axis ratio for a contact binary represented by identical biaxial ellipsoids, including the effects of shadowing of one component by the other. We compare the models with published high phase angle observations, and with interstellar object 1I/‘Oumuamua (Δm = 2.5 mag at a phase angle of α = 23°), finding an axis ratio of 5.2: 1 if represented as a single ellipsoid and 3.5: 1 for each component if represented as a nose-to-nose contact binary. While a detailed fit is not attempted, the comparison shows that the single ellipsoid model is better.

High abdominal adiposity and low phase angle in overweight renal transplant recipients.

Obesity is associated with increased risk of cardiovascular disease (CVD). Body mass index (BMI) is the most used parameter for obesity screening. However, the evaluation of CVD risk in overweight individuals should include the assessment of body fat distribution and body composition. Renal transplant recipients (RTR) have a high CVD risk and frequently present weight gain and loss of lean mass. The aim of this study was to evaluate body fat distribution and body composition in overweight RTR. This cross-sectional study was conducted with 86 RTR and 86 hypertensive individuals (comparison group, CG) presenting BMI 25-35Kg/m2 and 45-70years. Anthropometric evaluation included BMI, waist circumference, waist-to-height ratio, and a body shape index. Body composition was evaluated with bioelectrical impedance analysis (BIA). Glomerular filtration rate was estimated (eGFR) by CKD-EPI equation. RTR group (RTRG) and CG presented similar age and BMI. RTRG when compared to CG presented lower percentage of women and eGFR; higher central adiposity; and lower values of reactance, intracellular water, body cell mass and phase angle, more consistently observed in women. This study suggests that overweight RTR present higher abdominal adiposity and impairment in BIA parameters that are sensitive indicators of impaired membrane integrity, water distribution, and body cell mass.

Irreversible Demagnetization Analysis for Multilayer Magnets of Permanent Magnet-Assisted Synchronous Reluctance Machines Considering Current Phase Angle

This paper investigates the demagnetization problem of permanent magnets for permanent magnet-assisted synchronous reluctance motors (PMa-SynRM) and applies “demagnetization ratio” as an index to evaluate demagnetization of permanent magnet (PM). The PMa-SynRM is often designed with multilayer flux barriers to improve saliency and reluctance torque in the rotor. Weaker or less PM (than that for interior PM motors) is embedded into the rotor which could be demagnetized in high-performance operation. PM demagnetization involves temperature, current magnitude, current phase angle, designed PM operating point, or combined effect of the above factors. This work investigates the demagnetization risk for PMs in all the layers of PMa-SynRM rotor considering these factors. In particular, the current phase angle for flux weakening operation is often omitted in demagnetization analysis. First, the motor performance to satisfy the operation condition over a wide speed range is analyzed and the proportion of motor torque components, i.e., reluctance torque and electromagnetic torque, considering temperature is investigated. Then, the flux density distributions on PMs at each position/layer are studied and the PM operating points are obtained based on the variation of excitation current, current phase angle, and temperature in order to evaluate the demagnetization risk. The analysis suggests that the high current phase angle combining the effect of high temperature is the major cause of irreversible demagnetization. Finally, a method incorporating the index “demagnetization ratio” is proposed to redesign the PMa-SynRM to avoid demagnetization. Experiments are conducted to validate the simulation.

Combined analysis of miRNA-181a with phase angle derived from bioelectrical impedance predicts radiotherapy-induced changes in body composition and survival of male patients with head and neck cancer.

Nutritional deficits developing as an effect of applied radiotherapy (RTH) negatively affect patients' quality of life, survival, and therapy outcomes. We demonstrated novel approach to prediction of RTH-induced changes in body composition of patients with head and neck cancer using phase angle (PA) derived from bioelectrical impedance in combination with miRNA-181a expression. Patients with simultaneous presence of low PA and high miRNA expression were at a significantly higher risk of decreasing the fat-free mass index (FFMI) <14.9 kg/m2 (odds ratio [OR] = 5.14; P = .02), FFM < 44.7 kg (OR = 6.20; P = .04), and lean mass (OR = 10.0; P = .04) during the therapy period. Receiver operating curve analysis allowed to predict changes in FFMI, lean mass, and FFM with area under the curve calculation over 0.700. The simultaneous presence of high miRNA and low PA negatively affected patients' survival (OR = 5.12; P = .02). Evaluation of PA in combination with miRNA demonstrates higher diagnostic accuracy and predictive value for detecting RTH-induced changes in body composition of patients with cancer.

677-P: Bioimpedance Phase Angle in Diabetes and Change after an Interdisciplinary Care and Diabetes Self-Management Education Program

Bioimpedance phase angle (PA) is an index of cellular health and function, and a high PA suggest better cellular membrane integrity and a higher cell mass. PA has been identified as a valuable measurement for the diagnosis, monitoring and prognosis of various disorders. We evaluated baseline differences and change in PA in patients who attended a five months Interdisciplinary Care and Diabetes Self-management Education Program in a public primary care specialized diabetes clinic in Mexico City/Iztapalapa in 2018. In 327 persons with type 2 diabetes, PA was evaluated by bioelectrical impedance multifrequency analysis (Seca® 515/514, 50 Hz). Diabetes-related microvascular complications (MiVC) were defined by fundoscopy with mydriatic camera assessed by an ophthalmologist (retinopathy) and increased urine albumin/creatinine ratio and/or decreased estimated glomerular filtration rate (diabetic kidney disease). Women represented 67% and 56% had elementary or less education. Mean age was 55±10 years old, mean duration of diabetes was 12±8 years, 32.7% presented nephropathy and 24.8% retinopathy. Baseline PA was different among participants with or without MiVC (4.66±0.65 vs. 5.02±0.58, p&amp;lt;0.0001). Change in PA was different among participants with non-MiVC (5.02±0.58 to 5.11±0.62, p=&amp;lt;0.0001) but not among participants with MiVC (4.66±0.65 to 4.62±0.65, p=0.136) after the program. Diet self-care behavior improvement (2.6± 1.6 to 5.4±0.9 days/week, p=&amp;lt;0.001) and HbA1c reduction (9.45±2.0 to 6.7±1.2%, p=&amp;lt;0.001) were also observed with no differences among groups. Baseline PA was different according to the MiVC profile implying its prognosis and diagnosis role. PA improvement in persons with diabetes and absence of MiVC suggest a monitoring role of PA, but also suggest an added effect and the efficacy of this program since it favors the achievement of multiple diabetes care goals, that could be being reflected in PA as a marker of cellular integrity. Disclosure R. Silva-Tinoco: Speaker's Bureau; Self; Novo Nordisk Inc. T. Cuatecontzi-Xochitiotzi: None. L. Castillo-Martínez: None. P. León-García: None. D. Cabrera-Gerardo: None. J. Hernández: None. A. Ferreira-Hermosillo: Speaker's Bureau; Self; Sanofi, Takeda Mexico. C. Zárate: None. V.A. DeLaTorre-Saldaña: None.

Serendipitous infrared observations of Europa by Juno/JIRAM

We performed spectral analyses on four serendipitous observations of Europa acquired by the JIRAM instrument (Adriani et al., 2017) onboard the Juno mission. Due to the fixed orientation of the spacecraft spin axis and orbital plane placed along terminator, Europa is observed at approximately 90° phase angle from distances >3.35E5 km resulting in a best spatial resolution of 80 km/px. The one thousand spectra dataset returned to the ground offers a limited coverage in longitude but an almost complete excursion in latitude from poles to equator. With a 2 to 5 μm spectral range and a sampling of about 10 nm/band, JIRAM reflectance spectra allow extraction of different spectral indicators suitable to characterize surface composition, grain size distribution and temperature: the 2 μm water ice band center appears on average centered at 2.038 μm as a result of the presence of both amorphous and crystalline ice phases and non-ice materials. The reflectance level on the 2.4 μm inflection shoulder is comparable to the maximum absorption on the 2 μm band pointing to the presence of non-ice materials, like magnesium chlorinated or hydrated magnesium salts, mixed with water ice. Assuming water ice as the principal endmember, weestimate the surface regolith grain size by comparing the 2 μm band depth and the ratio between I/F at 3.63 and 2.27 μm (Filacchione et al., 2012). On average, we measure values of 0.6 for the first and 0.1 for the latter: such values are compatible with grain sizes in the range of tens to hundreds of microns. Despite the low signal-to-noise beyond 2.7 μm, due to the intrinsic low-reflectance of Europa's surface and very high phase angle values occurring during the observations, JIRAM is able to measure the wavelength of the reflectance peak around 3.6 μm, which is a proxy of water ice temperature (Filacchione et al., 2016a). In the dataset JIRAM has obtained the peak's maximum wavelength occurs at 3.64 μm corresponding to a maximum diurnal temperature of 132 K.

Phase Angle as an Objective and Predictive Factor of Radiotherapy-induced Changes in Body Composition of Male Patients With Head and Neck Cancer.

Unfavorable changes in body composition are frequent among patients with head and neck cancer (HNC). Unfortunately, in daily clinical practice, there is a lack of reliable diagnostic tools for predicting changes in body composition in individuals following radiotherapy (RT). Among non-invasive tools, bioelectrical impedance analysis (BIA) seems to be most promising. One BIA parameter, the phase angle (PA), reflects condition of various body cells and their mass in detail. Using BIA, the body composition was measured prior to and after RT in 52 male patients with HNC. PA derived from BIA prior to RT was tested as a predictor of body composition changes developing during RT. Patients with low PA had a greater than 9.3-fold higher chance of body mass index (BMI) reduction below 18.5 kg/m2 and over 5.9-fold and 4.2-fold higher chance of lean mass and fat mass reduction after therapy end compared with patients with a high PA value. PA values demonstrated significant diagnostic accuracy for detection of fat-free mass, lean mass and BMI reduction in the study group [area under the curve (AUC)=0.781, 0.774 and 0.786, respectively]. PA prior to RT is a useful marker for selection of individuals with HNC who are at a high risk of unfavorable changes in body composition.

Phase Angle Using Bioelectrical Impedance Analysis for Predicting Survival in Patients with Metastatic Cancer

Objectives The aim of this study was to identify the validity of phase angle as a prognostic factor for survival in patients with metastatic cancer. Methods Data of patients with metastatic cancer who visited the Korean medicine cancer center at Kyung Hee University Hospital in Gangdong from April 2016 to February 2018 were collected for this study. The values of phase angle (PhA) and blood hemoglobin (Hb), C-reactive protein (CRP), and serum albumin levels were also investigated by bioelectrical impedance analysis (BIA). Results In total, 86 patients were analyzed. The cut-off value of the phase angle was determined as 5.0. Univariate and multivariate analysis revealed that phase angle (HR 3.15, 95% CI 1.79-5.54) and CRP (HR 2.15, 95% CI 1.24-3.73) predicted survival with statistical significance. The median overall survival of the low PhA group (PhA≤5.0) was 1.8 months (95% CI 0.6-2.9 months) and 7.2 months (95% CI 5.2-9.2 months) in the high PhA group (PhA>5.0)(p<0.001). Conclusions The phase angle could be an independent prognostic factor for patients with metastatic cancer. Further research is required to confirm these findings and their correlation with other indexes. Keywords: bioelectrical impedence analysis (BIA), phase angle, palliative care, prognostic factor, metastatic cancer

Application of phase angle for evaluation of the nutrition status of patients with anorexia nervosa.

The evaluation of the nutrition status of patients has been the subject of interest of many scientific disciplines. Any deviation from normal values is a serious clinical problem. There are multiple nutrition status evaluation methods used including diet history, scales and questionnaires, physical examination, anthropometric measurements, biochemical measurements, function tests, as well as bioelectric impedance analysis or adipometry. Phase angle, obtained by means of bioelectric impedance analysis, is another parameter that is being more and more frequently applied in nutrition status monitoring. It is proportional to body cell mass. Its direct correlation with the cellular nutrition status has been documented. High phase angle values signify well-being, while low phase angle values indicate poor condition of cells. The purpose of this paper was to review the current state of knowledge about the application of phase angle in evaluation and monitoring of the nutrition status of patients with anorexia nervosa on the basis of available literature. It was proven that the phase angle values in patients with anorexia nervosa are much lower compared to healthy people. Detailed observations showed phase angle value increase in the course of treatment. The relevance of the commonly used body mass index (BMI) has been questioned due to significant degree of generalization in the nutrition status evaluation. Thus, there is a need for new, objective parameters for nutrition status evaluation, which will assist in the treatment and monitoring of patients in a more meaningful and reliable way. The existing independent studies equivocally confirm the usefulness of phase angle in the evaluation of nutrition status of patients with anorexia nervosa and its broader application in clinical practice is only a matter of time. However, these are merely attempts and they have not yet found wider application in clinical practice in the treatment of anorexia nervosa.

Particles Co-orbital to Janus and to Epimetheus: A Firefly Planetary Ring

Abstract The Cassini spacecraft found a new and unique ring that shares the trajectory of Janus and Epimetheus, co-orbital satellites of Saturn. Performing image analysis, we found this to be a continuous ring. Its width is between 30% and 50% larger than previously announced. We also verified that the ring behaves like a firefly. It can only be seen from time to time, when Cassini, the ring, and the Sun are arranged in a particular geometric configuration, in very high phase angles. Otherwise, it remains “in the dark,” invisible to Cassini’s cameras. Through numerical simulations, we found a very short lifetime for the ring particles, less than a couple of decades. Consequently, the ring needs to be constantly replenished. Using a model of particle production due to micrometeorites impacts on the surfaces of Janus and Epimetheus, we reproduce the ring, explaining its existence and the “firefly” behavior.

Eddy currents in the measurement of magnetic susceptibility of rocks

The in-phase and out-of-phase susceptibility of rocks is determined by the magnetic permeability of minerals, their viscous relaxation, and by eddy currents in electrically conductive minerals induced by the applied field. The last effect has been modelled by analytical solution of Maxwell equations for a conductive sphere immersed in a homogeneous, non-conductive medium with given permeability, in presence of an alternating field. The solution is a complex function of parameters describing the sphere (its size, conductivity and permeability), surrounding medium (permeability) and applied field (frequency). Without numerical evaluations, it is difficult to distinguish in-phase and out-of-phase (OPS) susceptibility. In this paper, approximate equations are derived for both susceptibility components, which depend only on the permeability contrast between the sphere and the surrounding medium, and the skin ratio, defined as the ratio between sphere radius and skin depth of the induced currents. These equations are used to obtain a systematic assessment of the role of electrical conductivity in determining the susceptibility of rock samples. The contribution of eddy currents to the susceptibility of diluted (<5%) magnetite particle dispersions is negligible at 1 kHz, but not at higher frequencies. Common rock-forming paramagnetic and diamagnetic minerals with weak electrical conductivity and magnetic permeability are characterized by negligible OPS at 1 kHz. Theoretically, measurable OPS and high phase angles can be produced by paramagnetic conductive minerals in certain combinations with a diamagnetic matrix. This can be excluded from practical point of view for paramagnetic minerals with susceptibilities >0.003 and conductivities not exceeding 5000 S/m.

Risk Factors for Pediatric Extubation Failure: The Importance of Respiratory Muscle Strength.

Respiratory muscle weakness frequently develops during mechanical ventilation, although in children there are limited data about its prevalence and whether it is associated with extubation outcomes. We sought to identify risk factors for pediatric extubation failure, with specific attention to respiratory muscle strength. Secondary analysis of prospectively collected data. Tertiary care PICU. Four hundred nine mechanically ventilated children. Respiratory measurements using esophageal manometry and respiratory inductance plethysmography were made preextubation during airway occlusion and on continuous positive airway pressure of 5 and pressure support of 10 above positive end-expiratory pressure 5 cm H2O, as well as 5 and 60 minutes postextubation. Thirty-four patients (8.3%) were reintubated within 48 hours of extubation. Reintubation risk factors included lower maximum airway pressure during airway occlusion (aPiMax) preextubation, longer length of ventilation, postextubation upper airway obstruction, high respiratory effort postextubation (pressure rate product, pressure time product, tension time index), and high postextubation phase angle. Nearly 35% of children had diminished respiratory muscle strength (aPiMax ≤ 30 cm H2O) at the time of extubation, and were nearly three times more likely to be reintubated than those with preserved strength (aPiMax > 30 cm H2O; 14% vs 5.5%; p = 0.006). Reintubation rates exceeded 20% when children with low aPiMax had moderately elevated effort after extubation (pressure rate product > 500), whereas children with preserved aPiMax had reintubation rates greater than 20% only when postextubation effort was very high (pressure rate product > 1,000). When children developed postextubation upper airway obstruction, reintubation rates were 47.4% for those with low aPiMax compared to 15.4% for those with preserved aPiMax (p = 0.02). Multivariable risk factors for reintubation included acute neurologic disease, lower aPiMax, postextubation upper airway obstruction, higher preextubation positive end-expiratory pressure, higher postextubation pressure rate product, and lower height. Neuromuscular weakness at the time of extubation was common in children and was independently associated with reintubation, particularly when postextubation effort was high.

Association of mortality and phase angle measured by different bioelectrical impedance analysis (BIA) devices

A high phase angle measured by the Nutriguard® bioelectrical impedance analysis device is associated with a reduced mortality risk in older people. This retrospective study aims to analyze whether this association persists with the other devices that have been used in our hospital. This study encompasses all people 65 yrs and older who underwent a phase angle measurement between 1990 and 2011 at the Geneva University Hospitals, with the RJL-101® (RJL Systems), Xitron 4000B® (Xitron Technologies), Eugedia® (Eugédia-Spengler) and Bio-Z® (Spengler). Diseases at the time of phase angle measurement were reported in the form of the Cumulative Illness Rating Scale. Date of death was retrieved until December 2012. Phase angle values were categorized into sex- and device-specific quartiles, where quartile 1 represents the lowest quartile and reference value. Cox regressions were performed to evaluate the association between phase angle quartiles and mortality. We considered 1878 people (969 women), of whom 1151 had died. In univariate sex-specific Cox regressions, the death risk decreased progressively as the phase angle quartile measured by the Bio-Z® or RJL-101® increased. The HR (95% CI) in quartile 4 was 0.36 (0.26, 0.50) and 0.38 (0.29, 052) in women and men measured with the Bio-Z® (both p<0.001), and 0.23 (0.14, 0.39) and 0.19 (0.10, 0.36) in women and men measured with the RJL-101® (both p<0.001). The association between phase angle and mortality persisted when adjusted for age, body mass index or co-morbidities. The small number of deaths in people who underwent a measurement by Eugedia® (n=93) or Xitron 4000B® (n=56) did not allow performing multivariate Cox regressions. Phase angle quartiles are associated with mortality in people aged ≥65 years when using the RJL-101® or Bio-Z device®.

Role of Epicardial Fat to Buffer Deformation and Vibration in Coronary Arteries

Objectives: To examine the putative physiologic role of epicardial fat to buffer the coronary arteries and to review the data on deformation and vibration in coronary arteries. Methods: OvidSP Medline, Embase, and PubMed were systematically searched. Eligible articles on vibration in arteries and deformation of coronary arteries were assessed. Results: Coronary arteries are unique because they undergo substantial deformations with twisting, bending, and stretching that are due to cardiac contraction and the tethering of the large coronary arteries to the epicardial surface of the heart. In addition, phasic coronary artery pressure and blood flow are not synchronous producing a high negative stress phase angle between circumferential strain and wall shear. Fluid flow–induced vibrations, a universal finding in conduits transporting fluid with pulsatile flow, have been documented in arteries. Arterial vibration can damage the structure of arterial wall, especially elastin and endothelial cells, leading to alterations in the arterial function. Support for a beneficial mechanical role for epicardial fat is based on the data that wrapping material to the outside of conduits not only reduces the vibration but also decreases their movement. The overall impact of an external wrap is a reduction in the probability of conduit fatigue and failure. Characteristics of the artery, such as shear modulus, are a function of the properties of each layer of the artery. The application of epicardial fat to the adventitia of arteries alters the biophysical characteristics of the artery which is the sum of each layer including the epicardial fat. Vibration, resonance, and deformation energy are lost when they hit the surface of an absorbing material. Conclusions: The integration of the biophysics of coronary arteries with knowledge of material damping principles supports a physiologic role for epicardial fat to buffer deformation and vibration in coronary arteries.

Use of oil in the polymerization of aniline to polyaniline salt containing dual dopants, sulfuric acid, and castor oil: material for high-performance supercapacitor

Supercapacitor is an important energy storage device. In this work, for the first time, oil (castor oil) is used instead of hazardous acids in the polymerization of aniline. This process yields polyaniline salt containing dual dopants, sulfuric acid, and castor oil. This castor oil is expected to interact with electrolyte in supercapacitor and thereby increases the electrochemical performance of supercapacitor. Polyaniline salt was synthesized by the oxidation of aniline in presence of castor oil instead of strong acid using ammonium peroxydisulfate oxidant via interfacial polymerization pathway. Formation of polyaniline salt was confirmed from IR, XRD analyses, and morphology studies from FE-SEM analyses. The results of this study showed the formation of nano-oblate/rod morphologies of semi-crystalline polyaniline salts, which show a specific capacitance value of 410 F g−1. Higher specific capacitance, cycle life, low charge transfer resistance, and high phase angle of polyaniline supercapacitor cell indicate a higher performance supercapacitor system.

One-step preparation of sulfonated carbon and subsequent preparation of hybrid material with polyaniline salt: a promising supercapacitor electrode material

The present trend to increase the energy density of electrochemical supercapacitor is to hybrid the electrochemical double layer capacitance electrode materials of carbon with loading or encapsulation of transition metal oxide or conductive polymeric pseudocapacitor materials as the binary or ternary hybrid electrochemical active materials. In this work, we selected polyaniline salt-sulfonated carbon hybrid (PANI-SA•C SA ) as a cheaper electrode material for supercapacitor electrode. Sulfonated carbon (C SA ) was prepared from hydrothermal carbonization of furaldehyde and p-toluenesulfonic acid. Polyaniline-sulfate salt containing sulfonated carbon was prepared by chemical oxidative polymerization of aniline using ammonium persulfate in presence of sulfuric acid and sulfonated carbon via aqueous, emulsion and interfacial polymerization pathways. Formation of hybrid material was confirmed from scanning electron microscopy. Among the hybrid prepared with three different polymerization pathways, hybrid prepared by aqueous polymerization pathway showed better electrochemical performance. The specific capacitance of the hybrid prepared via aqueous polymerization was 600 F g−1, which is higher than that of the pristine PANI-SA (350 F g−1) and C SA (30 F g−1). Hybrid material was subjected for 8000 charge-discharge cycles and at 8000 cycles; it showed 88% retention of its original specific capacitance value of 485 F g−1 with coulombic efficiency (97–100%). These results showed that C SA micro spheres prevent the degradation of PANI-SA chains during charge/discharge cycles. Specific capacitance, cycle life, low solution resistance, low charge transfer resistance and high phase angle value of PANI-SA•C SA supercapacitor cell indicates a higher performance supercapacitor system.

Dust particle flux and size distribution in the coma of 67P/Churyumov-Gerasimenko measured in situ by the COSIMA instrument on board Rosetta

Context. The COmetary Secondary Ion Mass Analyzer (COSIMA) on board Rosetta is dedicated to the collection and compositional analysis of the dust particles in the coma of 67P/Churyumov-Gerasimenko (67P). Aims. Investigation of the physical properties of the dust particles collected along the comet trajectory around the Sun starting at a heliocentric distance of 3.5 AU. Methods. The flux, size distribution, and morphology of the dust particles collected in the vicinity of the nucleus of comet 67P were measured with a daily to weekly time resolution. Results. The particles collected by COSIMA can be classified according to their morphology into two main types: compact particles and porous aggregates. In low-resolution images, the porous material appears similar to the chondritic-porous interplanetary dust particles collected in Earth’s stratosphere in terms of texture. We show that this porous material represents 75% in volume and 50% in number of the large dust particles collected by COSIMA. Compact particles have typical sizes from a few tens of microns to a few hundreds of microns, while porous aggregates can be as large as a millimeter. The particles are not collected as a continuous flow but appear in bursts. This could be due to limited time resolution and/or fragmentation either in the collection funnel or few meters away from the spacecraft. The average collection rate of dust particles as a function of nucleo-centric distance shows that, at high phase angle, the dust flux follows a 1/ d 2 comet law, excluding fragmentation of the dust particles along their journey to the spacecraft. At low phase angle, the dust flux is much more dispersed compared to the 1/ d 2 comet law but cannot be explained by fragmentation of the particles along their trajectory since their velocity, indirectly deduced from the COSIMA data, does not support such a phenomenon. The cumulative size distribution of particles larger than 150 μ m follows a power law close to r − 0.8 ± 0.1 , confirming measurements made by another Rosetta dust instrument Grain Impact Analyser and Dust Accumulator (GIADA). The cumulative size distribution of particles between 30 μ m and 150 μ m has a power index of −1.9 ± 0.3. The excess of dust in the 10–100 μ m range in comparison to the 100 μ m–1 mm range together with no evidence for fragmentation in the inner coma, implies that these particles could have been released or fragmented at the nucleus right after lift-off of larger particles. Below 30 μ m, particles exhibit a flat size distribution. We interprete this knee in the size distribution at small sizes as the consequence of strong binding forces between the sub-constitutents. For aggregates smaller than 30 μ m, forces stronger than Van-der-Waals forces would be needed to break them apart.

Near-infrared thermal emission from near-Earth asteroids: Aspect-dependent variability

Here we explore a technique for constraining physical properties of near-Earth asteroids (NEAs) based on variability in thermal emission as a function of viewing aspect. We present case studies of the low albedo, near-Earth asteroids (285263) 1998 QE2 and (175706) 1996 FG3. The Near-Earth Asteroid Thermal Model (NEATM) is used to fit signatures of thermal emission in near-infrared (0.8 - 2.5 µm) spectral data. This analysis represents a systematic study of thermal variability in the near-IR as a function of phase angle. The observations of QE2 imply that carefully timed observations from multiple viewing geometries can be used to constrain physical properties like retrograde versus prograde pole orientation and thermal inertia. The FG3 results are more ambiguous with detected thermal variability possibly due to systematic issues with NEATM, an unexpected prograde rotation state, or a surface that is spectrally and thermally heterogenous. This study highlights the potential diagnostic importance of high phase angle thermal measurements on both sides of opposition. We find that the NEATM thermal beaming parameters derived from our near-IR data tend to be of order10’s of percent higher than parameters from ensemble analyses of longer wavelength data sets. However, a systematic comparison of NEATM applied to data in different wavelength regimes is needed to understand whether this offset is simply a reflection of small number statistics or an intrinsic limitation of NEATM when applied to near-IR data. With the small sample presented here, it remains unclear whether NEATM modeling at near-IR wavelengths can robustly determine physical properties like pole orientation and thermal inertia.

Behavior of Passive Film on New Ti-Zr-Ta-Ag Alloy Surface in Simulated Biofluid

We elaborated a new Ti-20Zr-5Ta-2Ag alloy with innovative composition and properties to fulfil the necessities of corrosion resistance, biocompatibility and antibacterial protection; this alloy was complete and complex characterized: its microstructure by scanning electron microscopy (SEM); its native passive film by X-ray photoelectron spectroscopy (XPS); the surface wettability by contact angle measurements; the electrochemical behaviour in simulated human biofluid (Ringer solution of different pH values) by cyclic and linear polarization, electrochemical impedance spectroscopy (EIS) and monitoring of the open circuit potentials for 1000 exposure hours; the quantity of ions released in time by inductively coupled plasma-mass spectroscopy (ICP-MS). The new alloy has bi-phase, α + β, acicular microstructure, homogeneous and fine; also, lamellas of α and β phases, separated by distances of few microns can be observed (SEM images). Both survey and high resolution XPS spectra showed that the native passive film on Ti-20Zr-5Ta-2Ag alloy surface consists from the protective TiO2, ZrO2, Ta2O5 oxides, Ti and Ta suboxides and metallic Ag, which compact, reinforce and thicken the alloy passive film in comparison with that of Ti. The new alloy native passive film has a thickness of about 12 nm that is well above of that for Ti (1.3 – 3.7 nm). The contact angle for the new Ti-20Zr-5Ta-2Ag alloy has value of 64.54 0; it is a surface with high hydrophilic properties; its surface energy is 29.4 mJ/m2, representing a good value that promotes the interactions with biological fluids, cells and tissue and leads to a better biocompatibility. The corrosion and passivation potentials of the new alloy have more electropositive values than those of Ti, as result of the beneficial effect of Zr and Ta elements (which take part to the formation of the new alloy passive film, as XPS data showed) and of Ag that has a higher mixed potential. The passive current densities for Ti-20Zr-5Ta-2Ag alloy have lower values (of about 6 times) than those of Ti; corrosion current densities and rates are about 25-28 times lower and the polarisation resistances are about 21-28 times higher than those of Ti; this behaviour is due to the more protective passive layer existing on the new alloy surface. Nyquist spectra displayed capacitive loops associated with passive film like an insulator. Bode impedance spectra presented higher impedance values for the new alloy suggesting a more protective passive film than that on Ti surface. The new Ti-20Zr-5Ta-2Ag alloy exhibited higher phase angles than those for Ti, fact that demonstrates a nobler behaviour, a more capacitive film, a more resistant layer as result of its more compact, thicker, more complex composition. The impedance results were modelled with an electric equivalent circuit with two time constants corresponding to those two phase angles; the high phase angle represents a very capacitive, very resistant, barrier layer; the lower phase angle reflects the defective, less resistant, porous layer. The electrical parameters evinced slightly more unfavourable values for Ti, indicating that the passive film on its surface has lower insulating properties than the passive film on Ti-20Zr-5Ta-2Ag alloy surface; this fact is normal because the passive film on the new alloy surface is more compact, thicker, and, in addition, contains very protective ZrO2, Ta2O5 oxides, Ta suboxide and metallic Ag (as results from XPS data). The new Ti-20Zr-5Ta-2Ag alloy releases into Ringer solution low quantities of metallic ions, order of parts per million (ppm) beginning after 120 immersion hours; the quantity of the released ions increased over time. Silver ions were released in very low amount that enhanced in time, assuring long term antibacterial activity of the new alloy (ICP-MS data). The values of the open circuit potentials for the new Ti-20Zr-5Ta-2Ag alloy have more electropositive values than those of Ti, due to the alloy thicker, more compact (XPS results), more resistant (electrochemical and corrosion parameters) passive film. After about 500 immersion hours, all open circuit potential values tended to constant levels and maintained very constantly till 1000 hours, proving the alloy good stability. Open circuit potential differences had very low values situated under limits of 500 mV ÷ 600 mV necessary to form galvanic cells. Therefore, both Ti and new Ti-20Zr-5Ta-2Ag alloy are not susceptible to galvanic corrosion. The coupling of Ti with noble metals (Pt, Au, Ag) conducts to a higher mixed potential, because the noble metals are catalyst for the reducing both of the oxygen and water reactions. Thus, a quantity of 2% Ag is capable to increase the corrosion potentials of the new alloy.