1D Measurement Research Articles

Degradation Mechanism Study for Secondary Degradants in Rosuvastatin Calcium and Determination of Degradant Acetaldehyde Using Static Headspace Gas Chromatography Coupled with Matrix Precipitation

During the development of headspace gas chromatography (HSGC) method for assessing residual solvents in rosuvastatin calcium (RSV) drug substance, acetaldehyde (AA) was detected in obtained chromatograms, with a calculated concentration of up to 226 ppm. After a series of experiments, it was established that acetaldehyde originates from matrix interference due to direct degradation of Imp-C, which is accompanied by the formation of impurity at relative retention time (RRT) 2.18, without the involvement of impurity at RRT 2.31. The thermal instability of Imp-C also results in the formation of impurity at RRT 2.31 through dehydration and decarboxylation. In addition, cyclization reaction of degradant at RRT 2.18 further resulted in the generation of impurity at RRT 2.22. The structure of these three degradants, were confirmed by liquid chromatography-mass spectrometry (LC-MS), 1D and 2D nuclear magnetic resonance (NMR) measurement. In order to minimize the said matrix interference, a simple precipitation procedure was proposed as a pretreatment to mitigate the impact of Imp-C. Subsequently, an HSGC method was developed for the simultaneous determination of the degradant AA and the other five residual solvents used in RSV synthetic process. The final method was validated concerning precision, limit of detection (LOD) and limit of quantitation (LOQ), linearity, and accuracy.

H2-gas diffusion in porous media as observed by NMR

Not only is hydrogen (H2) the simplest and most abundant gas in our universe, it also plays a pivotal role in the decarbonization of our energy. As such hydrogen will be one of the most important critical enablers for industry in the global energy transition. Hydrogen’s low density hinders the wide-scale deployment and therefore, it is important to come to large scale low-cost H2 storage capacity as a source of hydrogen gas. In order, to store the energy in the TW h/GW h-range subsurface storage of hydrogen in depleted hydrocarbon reservoir and/or deep saline aquifers is needed. Concerning the hydrogen storage in depleted gas/oil reservoirs there are still many scientific questions open, which have to be addressed in order to come to reliable, efficient and cost-effective storage [1, 2]. For example, the injected hydrogen will displace the pore residual oil/gas and spread out in a reservoir; a trap structure is needed to prevent the hydrogen from escaping and allowing reproduction of the hydrogen, i.e., leakage is a major concern. Accurate predictions are needed of multi-phase fluid displacement in porous media, e.g., the interaction/displacement of cushion gas and the interactions with the solid matrix.
 In this study we have used NMR to image the diffusion and interaction in porous media. NMR is one the few methods by which H2-gas can be directly imaged in porous media. In order to do so, we have constructed a special NMR setup to measure the diffusion in porous media up to 60 bar. As the relaxation times measured for hydrogen are too short for 3D imaging this setup is limited to 1D measurement [3]. As, to be able to measure also on real porous media containing magnetic impurities, it was chosen to keep the main field at 0.7 T. The present setup is made up of an electromagnet generating a main magnetic field of 0.7 T with a gap of 70 mm and a picture is given in Fig 1. The NMR setup itself is equipped with Anderson gradient coils which can generate up to 0.3 T/m. An RF insert was made which is equipped with a special Faraday-shield, to be able to perform quantitative measurements and as such this setup is directed towards quantitative H2 profile measurements [4].
 For the NMR measurements a special PEEK reactor was purchased, which can be operated on up to 60 bars. The PEEK reactor has an outer diameter of 50 mm and inner diameter of 30 mm with a length of 500 mm. The reactor can be moved through the RF-coil with the help of a stepper motor, hence giving the possibility to measure the H2 content profile over the length of the reactor.
 In the initial tests we looked at the quantitative measurement of H2 as a function of the gas pressure. These initial measurements show that the H2 gas has a T1 in the order of 0.5 ms. Hence, as the signal of the H2 gas is quite low in comparison to the background noise, it was decided to measure the H2 gas at a high repetition rate, i.e., TR=2 ms. The results as function of the gas pressure up in the initial test upto 15 bars are given in Fig 2. As can be seen a clear linear behavior is found and only a minor contribution of the background is observed. In the next experiment the reactor was filled with 0.06 mm glass beads to mimic an ideal porous material and the results are also given in Fig 2. Again, a clear linear behavior can be observed, indicating measurements can also be performed in porous media.
 After this preliminary study in which we have tested the setup, we now intend to conduct measurements on porous glass beads up to 2 mm under various prewetting conditions, e.g., water, NaCl solution, oil and at various pressures. Here we want to measure the exchange of H2 gas by other gases such as N2 up to 60 bar and see the influence of the various prewetting conditions.

A structured FMEA approach to optimizing combinations of plan-specific quality assurance techniques for IMRT and VMAT QA.

Many commercial tools are available for plan-specific quality assurance (QA) of radiotherapy plans, with their functionality assessed in isolation. However, multiple QA tools are required to review the full range of potential errors. It is important to assess their effectiveness in combination with each other to look for ways to both streamline the QA process and to make certain that errors of high impact and/or high occurrence are caught before reaching patient treatment. To develop a structured method to assess the effective risk reduction of combinations of QA methods for IMRT/VMAT treatments. First, a structured prospective risk assessment was performed to establish the major failure modes (FMs) of IMRT/VMAT QA, and assign occurrence (O), severity (S), and baseline detectability (BD) rankings to them. The baseline assumed that chart checks and linear accelerator QA was performed, but no plan-specific secondary dose calculation or measurement was done. Second, the detectability of each FM for two secondary dose calculation methods and four plan measurement methods (point-based dose calculation, Monte-Carlo-based dose calculation, 2D fluence-based measurement, 2.5D phantom-based measurement, log file analysis with dose recalculation, and log file analysis combined with MLC QA) was determined. Third, we used a minimum detectability approach in addition to each FM's occurrence and severity to determine the optimal combination of QA methods.We analyzed the cumulative risk priority number of eight combinations of QA methods. The analysis was done on (1) all FMs, (2) FMs with high severity, (3) FMs with high-risk priority numbers (RPN) of O*S*BD, and (4) on FMs with both high severity and high RPN. Our analysis resulted in 54 FMs, including commissioning, planning, data transfer, and linear accelerator failures. 1D secondary dose calculation plus measurement provided a 19%-22% risk reduction from baseline. 1D/3D secondary dose calculation plus log files created a 25%-32% reduction. 3D secondary dose calculation plus measurement resulted in a 27%-34% reduction. 3D secondary dose calculation plus log files with additional machine QA provided the greatest reduction of 31%-42%. This novel structured approach to comparing combinations of QA methods will allow us to optimize our procedures, with the goal of detecting all clinically significant FMs. Our results show that log-file QA with 3D dose recalculation and supplemental machine QA provides better risk reduction than measurement-based QA. This work builds evidence to justify reducing or eliminating measurement-based PSQA with an independent 3D dose verification, log-file measurement, and appropriate supplementation of machine QA. The process also highlights FMs that cannot be caught by pre-treatment QA, prompting us to consider future directions for on-treatment QA.

High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters.

Laser light scattering systems with volume Bragg grating (VBG) filters, which act as spectral/angular filters, have often been used as a point measurement technique, with spatial resolution as low as a few hundred μm, defined by the beam waist. In this work, we demonstrate how VBG filters can be leveraged for spatially resolved measurements with several μm resolution over a few millimeters along the beam propagation axis. The rejection ring, as determined by the angular acceptance criteria of the filter, is derived analytically, and the use of the ring for 1D laser line rejection is explained. For the example cases presented,i.e., for a focused probe beam waist with a diameter of ∼150 μm, the rejection ring can provide resolution up to several millimeter length along the beam propagation axis for a 1D measurement, which is also tunable. Additionally, methods to further extend the measurable region are proposed and demonstrated, using a collimation lens with a different focal length or using multiple VBG filters. The latter case can minimize the scattering signal loss, without the tradeoff of the solid angle. Such use of multiple VBGs is to extend the measurable region along the beam axis, which differs from the commonly known application of multiple filters, to improve the suppression of elastic interferences. 1D rotational Raman and Thomson scattering measurements are carried out on pulsed and DC discharges to verify this method. The system features compactness, simple implementation, high throughput, and flexibility, to accommodate various experimental conditions.

1D versus 3D blood flow velocity and pulsatility measurements of lenticulostriate arteries at 7T MRI

Purpose7T MRI enables measurements of blood flow velocity waveforms in small, perforating cerebral arteries. As these vessels can be tortuous, acquisition methods sensitive to flow in only one direction may not be sufficient to accurately determine the dynamic blood flow velocity. In this study, we compared 1D with 3D velocity encoding to measure the blood flow velocity and pulsatility in the lenticulostriate arteries (LSAs). MethodsBlood flow velocity waveforms were measured in the LSAs of 18 subjects (age range: 20–74 years) using prospectively gated single-slice phase contrast (PC) MRI at 7T. For each subject, blood flow velocity waveforms were acquired in a single slice with one velocity encoding as well as three orthogonal velocity encodings. The peak velocity and pulsatility index (PI) were determined in the largest, perpendicularly planned LSA, one obliquely planned LSA and three smaller LSAs. The peak velocity and PI were compared between 1D and 3D measurements using Bland-Altman analysis, with the 95% limits of agreement (LOA) taken into account. ResultsFor the largest, perpendicularly planned LSA, the peak velocity was slightly lower (0.2 cm/s, 1.7%) for 1D compared to 3D measurements, with an LOA range from the mean difference of (−0.27;0.27). The PI was slightly higher (0.01, 1.6%) for the 1D measurement, and an LOA range from the mean difference in PI of (−0.045;0.045). The obliquely planned LSA and three smaller LSAs demonstrated larger deviations (range mean percentage difference: 3.9–8.2%). Conclusion1D velocity encoding using 2D PC MRI provides sufficiently accurate dynamic velocity and pulsatility measurements in slices perpendicularly planned to single, large LSAs compared to 3D velocity encoding, while increasing errors are obtained with obliquely planned slices. A greater error is indicated when measuring multiple (possibly tortuous or obliquely planned) smaller LSAs in one scan using one-directional single-slice PC MRI.

O2 based resonantly ionized photoemission thermometry analysis of supersonic flows.

Characterization of the thermal gradients within supersonic and hypersonic flows is essential for understanding transition, turbulence, and aerodynamic heating. Developments in novel, impactful non-intrusive techniques are key for enabling flow characterizations of sufficient detail that provide experimental validation datasets for computational simulations. In this work, Resonantly Ionized Photoemission Thermometry (RIPT) signals are directly imaged using an ICCD camera to realize the techniques 1D measurement capability for the first time. The direct imaging scheme presented for oxygen-based RIPT (O2 RIPT) uses the previously established calibration data to direct excite various resonant rotational peaks within the S-branch of the C3Π, (v = 2) ← X3Σ(v' = 0) absorption band of O2. The efficient ionization of O2 liberates electrons that induce electron avalanche ionization of local N2 molecules generating N2 +, which primarily deexcites via photoemissions of the first negative band of N2+(B 2 Σ u+-X 2 Σ g+). When sufficient lasing energy is used, the ionization region and subsequent photoemission signal is achieved along a 1D line thus, if directly imaged can allow for gas temperature assignments along said line; demonstrated here of up to five centimeters in length. The temperature gradients present within the ensuing shock train of a supersonic under expanded free jet serves as a basis of characterization for this new RIPT imaging scheme. The O2 RIPT results are extensively compared and validated against well-known and established techniques (i.e., CARS and CFD). The direct imaging capability fully realizes the technique's fundamental potential and is expected to be the standard of implementation going forward. The direct imaging capability can play instrumental roles in future scientific studies that rely upon acute characterization of thermal gradients within a medium that cannot be easily resolved by a point. Furthermore, the removal of the spectrometer greatly reduces the cost, complexity, and optical alignment associated with prior RIPT measurements.

Fast hyperspectral single-pixel imaging via frequency-division multiplexed illumination.

Hyperspectral imaging that detects 3D spectra-spatial information has been used in a wide range of applications. Among reported techniques, multiplexed spectral imaging with a single-pixel detector provides as a photon-efficient and low-cost implementation; however, the previous spectral modulation schemes are mostly complicated and sacrifice the imaging speed. Here, we propose a fast and compact hyperspectral single-pixel imaging technique based on programmable chromatic illumination. A multi-wavelength LED array modulated by independent carriers achieves stable and accurate spectral modulation up to MHz in a frequency-division multiplexed manner, hence allowing the full use of the spatial light modulation speed. Additionally, we propose a multi-channel deep convolutional autoencoder network to reconstruct hyperspectral data from highly-compressed 1D measurement. Experimental reconstructions of 12 spectral channels and 64 × 64 pixels are demonstrated for dynamic imaging at 12 fps image rate. The proposed imaging scheme is highly extensible to a wide spectrum range, and holds potential for portable spectral imagers in low-light or scattering applications.

Which evaluation criteria of the short-term efficacy can better reflect the long-term outcomes for patients with nasopharyngeal carcinoma?

PurposeTo compare the consistency of one-dimensional Response Evaluation Criteria in Solid Tumors (1D-RECIST), two-dimensional WHO criteria (2D-WHO), and three-dimensional (3D) measurement for therapeutic response assessment of nasopharyngeal carcinoma (NPC). Materials and methodsRetrospective data of 288 newly diagnosed NPC patients were reviewed. Tumor size was assessed on magnetic resonance imaging (MRI) according to the 1D-RECIST, 2D-WHO, and 3D measurement criteria. Agreement between tumor responses was assessed using unweighted k statistics. The receiver operating characteristic (ROC) curve was used to determine the optimal cut-off point of the PTV. The Kaplan–Meier method and Cox regression were used for the survival analysis. ResultsThe optimal cut-off point of the PTV for progression-free survival (PFS) was 29.6%. Agreement with PTV measurement was better for 1D measurement than for 2D and 3D measurements (kappa values of 0.646, 0.537, and 0.577 for 1D, 2D, and 3D measurements, respectively; P < 0.05). The area under the curve of the 1D measurement (AUC=0.596) was similar to that of the PTV measurement (AUC=0.621). Compared with 2D and 3D measurements, 1D measurement is superior for predicting prognosis in NPC (C-index of 0.672, 0.663, and 0.646 were for 1D, 2D, and 3D measurements, respectively; P < 0.005). Survival analysis showed that patients with non-responders had worse prognosis (P < 0.05). ConclusionsThe 1D measurement more closely agreed with the PTV measurement than the 2D and 3D measurements for predicting therapeutic responses in NPC. Therefore, we recommend using the less time-consuming 1D-RECIST criteria in routine clinical practice.

Guiding the design of superresolution tactile skins with taxel value isolines theory.

Tactile feedback is essential to make robots more agile and effective in unstructured environments. However, high-resolution tactile skins are not widely available; this is due to the large size of robust sensing units and because many units typically lead to fragility in wiring and to high costs. One route toward high-resolution and robust tactile skins involves the embedding of a few sensor units (taxels) into a flexible surface material and the use of signal processing to achieve sensing with superresolution accuracy. Here, we propose a theory for geometric superresolution to guide the development of tactile sensors of this kind and link it to machine learning techniques for signal processing. This theory is based on sensor isolines and allows us to compute the possible force sensitivity and accuracy in contact position and force magnitude as a spatial quantity before building a sensor. We evaluate the influence of different factors, such as elastic properties of the material, structure design, and transduction methods, using finite element simulations and by implementing real sensors. We empirically determine sensor isolines and validate the theory in two custom-built sensors with 1D and 2D measurement surfaces that use barometric units. Using machine learning methods to infer contact information, our sensors obtain an average superresolution factor of over 100 and 1200, respectively. Our theory can guide future tactile sensor designs and inform various design choices.

About 3D Incompressible Flow Reconstruction from 2D Flow Field Measurements.

In this paper, an assessment of the uncertainty affecting a hybrid procedure (experimental/numerical) is carried out to validate it for industrial applications, at the least. The procedure in question serves to depict 3D incompressible flow fields by using 2D measurements of it and computing the third velocity component by means of the continuity equation. A quasi-3D test case of an incompressible flow has been inspected in the wake of a NACA 0012 airfoil immersed in a forced flow of water running in a rectangular open channel. Specifically, starting from a 2D measurement data in planes orthogonal to the stream-wise direction, the computational approach can predict the third flow velocity component. A 3D ADV instrument has been utilized to measure the flow field, but only two velocity components have been considered as measured quantities, while the third one has been considered as reference with which to compare the computed component from the continuity equation to check the accuracy and validity of the hybrid procedure. At this aim, the uncertainties of the quantities have been evaluated, according to the GUM, to assess the agreement between experiments and predictions, in addition to other metrics. This aspect of uncertainty is not a technical sophistication but a substantial way to bring to the use of a 1D and 2D measurement system in lieu of a 3D one, which is costly in terms of maintenance, calibration, and economic issues. Moreover, the magnitude of the most relevant flow indicators by means of experimental data and predictions have been estimated and compared, for further confirmation by means of a supervised learning classification. Further, the sensed data have been processed, by means of a machine learning algorithm, to express them in a 3D way along with accuracy and epoch metrics. Two additional metrics have been included in the effort to show paramount interest, which are a geostatistical estimator and Sobol sensitivity. The statements of this paper can be used to design and test several devices for industrial purposes more easily.

Development of Glass-Tube-Pair Type Doppler Probe Array for 1D Profile Measurement of Two Component Ion-Flow Vector

We developed a new glass-tube-pair type Doppler probe array for 1D ion velocity vector and temperature measurement. It needs just two parallel glass-tube insertion, realizing low plasma perturbation and 1D ion flow vector measurement on a single discharge. Using four mirrors and optical fibers for one measurement point, this system can measure ion local light emissions of each measurement volume from four different directions, enabling us to measure local ion flow vector and temperature. All set of mirrors and optical fibers are aligned in the two parallel glass tubes for 1D measurement by a single discharge. This system measured successfully ion outflow speed of two merging tokamak plasmas, about 80% of poloidal Alfvén speed in agreement with recent reconnection experiments and theory.

Theory, method, and test tools for determination of 3D MTF characteristics in cone-beam CT.

The modulation transfer function (MTF) is widely used as an objective metric of spatial resolution of medical imaging systems. Despite advances in capability for three-dimensional (3D) isotropic spatial resolution in computed tomography (CT) and cone-beam CT (CBCT), MTF evaluation for such systems is typically reported only in the axial plane, and practical methodology for assessment of fully 3D spatial resolution characteristics is lacking. This work reviews fundamental theoretical relationships of two-dimensional (2D) and 3D spread functions and reports practical methods and test tools for analysis of 3D MTF in CBCT. Fundamental aspects of 2D and 3D MTF measurement are reviewed within a common notational framework, and three MTF test tools with analysis code are reported and made available online (https://istar.jhu.edu/downloads/): (a) a multi-wire tool for measurement of the axial plane MTF [denoted as , where is the measurement angle out of the axial plane] as a function of position in the axial plane; (b) a wedge tool for measurement of the MTF in any direction in the 3D Fourier domain [e.g., =45°, denoted as ]; and (c) a sphere tool for measurement of the MTF in any or all directions in the 3D Fourier domain. Experiments were performed on a mobile C-arm with CBCT capability, showing that yields an informative one-dimensional (1D) representation of the overall 3D spatial resolution characteristics, capturing important characteristics of the 3D MTF that might be missed in conventional analysis. The effects of anisotropic filters and detector readout mode were investigated, and the extent to which a system can be said to provide "isotropic" resolution was evaluated by quantitative comparison of MTF at various . All three test tools provided consistent measurement of , and the wedge and sphere tools demonstrated how measurement of the MTF in directions outside the axial plane ( ) can reveal spatial resolution characteristics to which conventional axial MTF measurement is blind. The wedge tool was shown to reduce statistical measurement error compared to the sphere tool due to improved sampling, and the sphere tool was shown to provide a basis for measurement of the MTF in any or all directions (outside the null cone) from a single scan. The C-arm system exhibited non-isotropic spatial resolution with conventional non-isotropic 1D apodization filters (i.e., frequency cutoff filters) - which is common in CBCT - and implementation of isotropic 2D apodization yielded quantifiably isotropic MTF. Asymmetric pixel binning modes were similarly shown to impart non-isotropic effects on the 3D MTF, and the overall 3D MTF characteristics were evident in each case with a single, 1D measurement of the 1D ). Three test tools and corresponding MTF analysis methods were presented within a consistent framework for analysis of 3D spatial resolution characteristics in a manner amenable to routine, practical measurements. Experiments on a CBCT C-arm validated many intuitive aspects of 3D spatial resolution and quantified the extent to which a CBCT system may be considered to have isotropic resolution. Measurement of ) provided a practical 1D measure of the underlying 3D MTF characteristics and is extensible to other CT or CBCT systems offering high, isotropic spatial resolution.

Structure elucidation and formation mechanistic study of a methylene-bridged pregabalin dimeric degradant in pregabalin extended-release tablets.

During the pharmaceutical development of pregabalin extended-release tablets, an unknown degradant at a relative retention time (RRT) of 11.7 was observed and its nominal amount exceeded the ICH identification threshold in an accelerated stability study. The aim of this study is to identify the structure and investigate the formation mechanism of this impurity for the purpose of developing a chemically stable pharmaceutical product. By utilizing multi-stage LC-MS analysis in conjunction with mechanism-based stress study, the structure of the RRT 11.7 impurity was rapidly identified as a dimeric degradant that is caused by dimerization of two pregabalin molecules with a methylene bridging the two pregabalin moieties. The structure of the dimer was confirmed by 1D and 2D NMR measurement. The formation pathway of the dimeric degradant was also inferred from the mechanism-based stress study, which implicated that the bridging methylene could originate from formaldehyde which might be the culprit that triggers the dimerization in the first place. The subsequent API-excipients compatibility study indicated that the degradant was indeed formed in the compatibility experiments between pregabalin API and two polymeric excipients (PEO and PVPP) that are known to contain residual formaldehyde, but only in the co-presence of another excipient, colloidal silicon dioxide (SiO2). The kinetic behavior of the degradant formation was also investigated and two kinetic models were utilized based on the Arrhenius and Eyring equations, respectively, to calculate the activation energy (Ea) as well as the enthalpy of activation (△H‡), entropy of activation (△S‡), and Gibbs free energy (△G‡) of the degradation reaction. The results of this study would be useful for the understanding of similar dimeric degradant formation in finished products of drug substances containing primary or secondary amine moieties.

An adaptive parameterization for efficient material acquisition and rendering

One of the key ingredients of any physically based rendering system is a detailed specification characterizing the interaction of light and matter of all materials present in a scene, typically via the Bidirectional Reflectance Distribution Function (BRDF). Despite their utility, access to real-world BRDF datasets remains limited: this is because measurements involve scanning a four-dimensional domain at sufficient resolution, a tedious and often infeasibly time-consuming process. We propose a new parameterization that automatically adapts to the behavior of a material, warping the underlying 4D domain so that most of the volume maps to regions where the BRDF takes on non-negligible values, while irrelevant regions are strongly compressed. This adaptation only requires a brief 1D or 2D measurement of the material's retro-reflective properties. Our parameterization is unified in the sense that it combines several steps that previously required intermediate data conversions: the same mapping can simultaneously be used for BRDF acquisition, storage, and it supports efficient Monte Carlo sample generation. We observe that the above desiderata are satisfied by a core operation present in modern rendering systems, which maps uniform variates to direction samples that are proportional to an analytic BRDF. Based on this insight, we define our adaptive parameterization as an invertible, retro-reflectively driven mapping between the parametric and directional domains. We are able to create noise-free renderings of existing BRDF datasets after conversion into our representation with the added benefit that the warped data is significantly more compact, requiring 16KiB and 544KiB per spectral channel for isotropic and anisotropic specimens, respectively. Finally, we show how to modify an existing gonio-photometer to provide the needed retro-reflection measurements. Acquisition then proceeds within a 4D space that is warped by our parameterization. We demonstrate the efficacy of this scheme by acquiring the first set of spectral BRDFs of surfaces exhibiting arbitrary roughness, including anisotropy.

Rheo-NMR of transient and steady state shear banding under shear startup

In this work, shear band formation following shear startup as a function of flow protocol is investigated in the wormlike micelle (WLM) system of 6 wt. % cetylpyridinium chloride and sodium salicylate in 0.5M NaCl brine in a Couette Rheo-nuclear magnetic resonance (NMR) shear cell. Many applications using WLM solutions occur under time dependent conditions; however, shear banding under time dependent flow protocols is not as well characterized. 1D velocity profiles across the 1 mm fluid gap are recorded every 1 s after shear startup using Rheo-NMR velocimetry and used to evaluate shear banding characteristics, including the shear rates in the low and high shear band, the interface position, and the apparent wall slip as a function of time. The velocity, and therefore the shear banding characteristics, exhibits large temporal fluctuations following an abrupt startup to 12 s−1. Data were decomposed into an average and fluctuation about the average in order to extract the characteristic time scales for the transition of the flow from transient to steady state. In addition, the Fourier transform of time autocorrelation functions was used to quantify the fluctuation frequencies themselves, which are related to the apparent slip at the inner rotating wall and the presence of flow instabilities. This analysis has the potential to allow a 1D measurement to provide information about the 3D flow. Shear startup experiments were also performed for flow protocols with and without preshear. Preshear resulted in different magnitudes of the timescales and a shift in the frequencies of the fluctuation of all shear banding characteristics, emphasizing the importance of shear history on the flow behavior of these WLM solutions.

Single-sided NMR for the diagnosis of osteoporosis: Diffusion weighted pulse sequences for the estimation of trabecular bone volume fraction in the presence of muscle tissue

The bone volume fraction, defined as the Bone-Volume-To-Total-Volume ratio (BV/TV), is an important parameter in the assessment of the bone's micro-structure, and is related to the fracture risk in osteoporosis. Although Magnetic Resonance Imaging (MRI) can assess bone micro-architecture parameters in-vivo, high-field whole body MRI scanners are hardly suitable for wide-scale screening campaigns. Recently, a new NMR application to assess in laboratory the BV/TV of trabecular bone (TB) has been proposed using low-field single-sided NMR. This paper presents an improvement of this technique that allows detection of only the signal from the marrow in the TB suppressing signals from other tissues, which may be present in the sensitive volume of single-sided scanners in a real scenario. The improvement was achieved by filtering signal acquisition by molecular diffusion. Experiments based on an ad-hoc designed Diffusion Weighted T1−T2 pulse sequence have demonstrated that muscle and cartilage signals can be suppressed by using diffusion weighting. On the basis of those experiments, a 1D measurement was established to allow correct estimation of the BV/TV of a TB sample also in the presence of muscle tissue in the sensitive volume of the NMR-scanner. The experiments presented, carried out with the NMR-MOUSE PM10 and the NMR-MOLE, exploiting diffusion-weighted pulse sequences, may pave the way for the in-vivo BV/TV evaluation using single-sided scanners.

Multispectral imaging using a single bucket detector.

Existing multispectral imagers mostly use available array sensors to separately measure 2D data slices in a 3D spatial-spectral data cube. Thus they suffer from low photon efficiency, limited spectrum range and high cost. To address these issues, we propose to conduct multispectral imaging using a single bucket detector, to take full advantage of its high sensitivity, wide spectrum range, low cost, small size and light weight. Technically, utilizing the detector’s fast response, a scene’s 3D spatial-spectral information is multiplexed into a dense 1D measurement sequence and then demultiplexed computationally under the single pixel imaging scheme. A proof-of-concept setup is built to capture multispectral data of 64 pixels × 64 pixels × 10 wavelength bands ranging from 450 nm to 650 nm, with the acquisition time being 1 minute. The imaging scheme holds great potentials for various low light and airborne applications, and can be easily manufactured as production-volume portable multispectral imagers.

Three-state analytic theory of two-dimensional nuclear magnetic resonance in systems with coupled macro- and micropores.

Two-dimensional (2D) nuclear magnetic resonance (NMR) experiments involve a sequence of longitudinal (T(1)) and transverse (T(2)) measurements. In a previous paper we showed that if each of these 1D measurements can be represented by two exponential decays then there can be an accurate analytic solution for the 2D measurements with no additional information. In this paper we extend the theory to the case where there are three decay channels for the 1D measurements. The resulting analytic theory introduces a single free parameter, which is a rotation angle in the vector space spanned by the normal modes. Our predictions agree quite well with numerical results based on the microporous grain consolidation (μGC) model. The theory allows one to deduce information about decay modes in situations in which they may not be measurable in a conventional 1D measurement because the amplitude of that mode is too small.

Characterization of air-cooled heat transfer using round and slot nozzles

Many industrial facilities, such as the widely used cooling tower, transfer heat to the atmosphere. The most common cooling media are water and air. The performance of cooling equipment depends upon such factors as flow rate, pressure at the nozzle tip, and the type of nozzle. In this article, round and slot nozzles with air as the cooling medium are studied to verify their cooling effectiveness. The heat transfer characteristics of these nozzles, compared using three different methodologies, are presented. A commercial computational fluid dynamics tool, FLUNET, is employed to model the 3D thermal-fluidic field of each nozzle. A 1D source code is also implemented in FORTRAN to achieve a faster and more reliable solution. Finally, experimental data are used to verify the two computational results. The difference between the results obtained using the FORTRAN code and FLUENT was about 0.07%. The temperatures at the cooling tower exit for the 1D and 3D codes were 431.9°C and 432.2°C (809.4°F and 810°F), respectively. Four sets of experimental data were compared with the numerical results. The maximum temperature difference between the 1D model and the measurements occurred at an inlet temperature of 450°C (842°F) and at a strip thickness of 2.28 mm. The outlet temperature from the 1D model and measurement was, respectively, 290.1°C and 278.5°C (554.2°F and 533.3°F), differing by approximately 4%. The 1D model generates good temperature predictions compared to measurements from a real cooling tower. This result would be very beneficial for industries that require fast temperature information for stable and steady operation, such as steelworks.

1D Measurement of Sodium Ion Flow in Hydrogel After a Bath Concentration Jump.

NMR is used to measure sodium flow driven by a 1D concentration gradient inside poly-acrylamid (pAA) hydrogel. A sodium concentration jump from 0.5 M NaCl to 0 M NaCl is applied at the bottom of a cylindrical pAA sample. The sodium level and hydrogen level are measured as a function of time and position inside the sample for 5 days. Then a reversed step is applied, and ion flow is measured for another 5 days. During the measurement, the cylindrical sample is radially confined and allowed to swell in the axial direction. At the same time, sodium and moisture in the sample are measured on a 1D spatial grid in the axial direction. A quadriphasic mixture model (Huyghe and Janssen in Int J Eng Sci 35:793, 1997) is used to simulate the results and estimate the diffusion coefficient of sodium and chloride. The best fit results were obtained for D_{Na^+} = 1.15times 10^{-5} cm2/s and D_{Cl^-} = 2.15times 10^{-5} cm2/s, at 25 degrees centigrade. Different time constants were observed for swelling and deswelling.