Hundreds Of Pa Research Articles

Generation of Radiation on Forbidden Transitions in the Laboratory Acoustic Plasma

Experimentally, under laboratory conditions in the nitrogen acoustic plasma in the region of the forbidden lines at 654.81 and 658.36 nm, a spectral emission line of high intensity was obtained (up to 17 stronger than the neighboring lines of the first positive system of nitrogen). The results were obtained both in pure low-pressure nitrogen acoustic plasma (several hundreds of Pa) and various mixtures containing nitrogen, including the CO2 : N2 : He = 1 : 1 : 8 mixture. The results obtained are explained by the acoustic plasma state of the discharge and an analog of Rahman scattering, which remove some of the quantum mechanical prohibitions. The possible influence of the Coriolis force is also considered.

Volcano Opto‐Acoustics: Mapping the Infrasound Wavefield at Yasur Volcano (Vanuatu)

AbstractWe explore the capabilities of volcano opto‐acoustics, a promising technique for measuring explosion and infrasound resonance phenomena at open‐vent volcanoes. Joint visual and infrasound study at Yasur Volcano (Vanuatu) demonstrate that even consumer‐grade cameras are capable of recording infrasound with high fidelity. Passage of infrasonic waves, ranging from as low as 5 Pa to hundreds of Pa, from both explosions and persistent tremor, pressurizes and depressurizes ambient plumes inducing visible vaporization and condensation respectively. Optical tracking of these pressure wavefields can be used to identify spectral characteristics, which vary within Yasur's two deep craters and are distinct for explosion and tremor sources. Wavefield maps can illuminate the propagation of blasts as well as the dynamics of persistent infrasonic tremor associated with standing waves in the craters. We propose that opto‐acoustic monitoring is useful for extraction of near‐vent infrasound signal and for tracking volcanic unrest from a remote distance.

Thermal Tides in the Martian Atmosphere Near Northern Summer Solstice Observed by ACS/TIRVIM Onboard TGO

AbstractThermal tides in the Martian atmosphere are analyzed using temperature profiles retrieved from nadir observations obtained by the TIRVIM Fourier‐spectrometer, part of the Atmospheric Chemistry Suite onboard the ExoMars Trace Gas Orbiter. The data is selected near the northern summer solstice at solar longitude (LS) 75°–105° of Martian Year 35. The observations have a full local time coverage, which enables analyses of daily temperature anomalies. The observed zonal mean temperature is lower by 4–6 K at ∼100 Pa, but higher toward the summer pole, compared to the Laboratoire de Météorologie Dynamique (LMD) Mars General Circulation Model (GCM). Wave mode decomposition shows dominant diurnal tide and important semi‐diurnal tide and diurnal Kelvin wave, with maximal amplitudes of 5, 3, and 2.5 K, respectively, from tens to hundreds of Pa. The results generally agree well with the LMD Mars GCM, but with noticeable earlier phases of diurnal (∼1 hr) and semi‐diurnal (∼3 hr) tides.

3D magnetically controlled spatiotemporal probing and actuation of collagen networks from a single cell perspective.

Cells continuously sense and react to mechanical cues from their surrounding matrix, which consists of a fibrous network of biopolymers that influences their fate and behavior. Several powerful methods employing magnetic control have been developed to assess the micromechanical properties within extracellular matrix (ECM) models hosting cells. However, many of these are limited to in-plane sensing and actuation, which does not allow the matrix to be probed within its full 3D context. Moreover, little attention has been given to factors specific to the model ECM systems that can profoundly influence the cells contained there. Here we present methods to spatiotemporally probe and manipulate extracellular matrix networks at the scale relevant to cells using magnetic microprobes (μRods). Our techniques leverage 3D magnetic field generation, physical modeling, and image analysis to examine and apply mechanical stimuli to fibrous collagen matrices. We determined shear moduli ranging between hundreds of Pa to tens of kPa and modeled the effects of proximity to rigid surfaces and local fiber densification. We analyzed the spatial extent and dynamics of matrix deformation produced in response to magnetic torques on the order of 10 pNm, deflecting fibers over an area spanning tens of micrometers. Finally, we demonstrate 3D actuation and pose extraction of fluorescently labelled μRods.

Micro-Area Ferroelectric, Piezoelectric and Conductive Properties of Single BiFeO₃ Nanowire by Scanning Probe Microscopy.

Ferroelectric nanowires have attracted great attention due to their excellent physical properties. We report the domain structure, ferroelectric, piezoelectric, and conductive properties of bismuth ferrite (BFO, short for BiFeO3) nanowires characterized by scanning probe microscopy (SPM). The X-ray diffraction (XRD) pattern presents single phase BFO without other obvious impurities. The piezoresponse force microscopy (PFM) results indicate that the nanowires possess a multidomain configuration, and the maximum piezoelectric coefficient (d33) of single BFO nanowire is 22.21 pm/V. Poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrate that there is sufficient polarization switching behavior and obvious piezoelectric properties in BFO nanowires. The conducting atomic force microscopy (C-AFM) results show that the current is just hundreds of pA at 8 V. These lay the foundation for the application of BFO nanowires in nanodevices.

Numerical study on flow characteristics and heat transfer enhancement of oscillatory flow in a spirally corrugated tube

The flow and heat transfer characteristics of oscillatory flow in a smooth tube and two-start spirally corrugated tube were investigated by using a three-dimensional unsteady numerical simulation. The simulation was performed under variable properties, pressure and velocity conditions, with helium (He) as the working medium. The results indicated that longitudinal swirl vortexes were generated with the guidance of a spirally corrugated channel in a two-start spirally corrugated tube in which the fluid flowed spirally forward. The heat absorption (Q) of a two-start spirally corrugated tube exceeded that of a smooth tube (Q0). The difference in the average heat absorption was 561 W and the average of Q/Q0 was 1.36. At the same inlet and wall temperatures of 575 K and 1000 K, the outlet temperature of the smooth and spirally corrugated tube increased by 205 K and 365 K, respectively. Therefore, the spirally corrugated tube presented a superior heat transfer performance when compared to that of the smooth tube. Two types of performance evaluation criterion (PEC) calculation methods in a cycle were used to evaluate the heat transfer enhancement of a spirally corrugated tube. The average value of transient PEC in a cycle was 1.69, and the PEC calculated by average parameters in a cycle was 1.38. When compared with the change of pressure in a MPa level in a heating tube, the pressure drop of hundreds of Pa was negligible. However, the outlet temperature of the heating tube could be subject to an additional temperature increase of hundreds of K with the negligible pressure drop of hundreds of Pa. Thus, the benefits were apparent for the heat transfer enhancement by using spirally corrugated tubes in the heater.

High-efficiency detector of secondary and backscattered electrons for low-dose imaging in the ESEM

A new Combined System for high-efficiency detection of Secondary and Backscattered Electrons (CSSBE) in the ESEM consists of three detectors: an ionisation SE detector, an improved scintillation BSE detector, and a new Ionisation Secondary Electron Detector with an electrostatic Separator (ISEDS). The ISEDS optimizes conditions for electron-gas ionisation phenomena in the ESEM to achieve a strongly amplified signal from the secondary electrons with a minimal contribution from backscattered and beam electrons. For this purpose, it is originally equipped with an electrostatic separator, which focuses signal electrons towards a detection electrode and controls the concentration of positive ions above the sample. The working principle of the ISEDS is explained by simulations of signal electron trajectories in gas using the EOD program with our Monte Carlo module. The ability to detect the signal electrons in a selected range of energies is described with Geant4 Monte Carlo simulations of electron-solid interactions and proven by experimental results. High-efficiency detection of the ISEDS is demonstrated by imaging a low atomic number sample under a reduced beam energy of 5 keV, very low beam currents of up to 0.2 pA, and gas pressure of hundreds of Pa.

Different TCR-induced T lymphocyte responses are potentiated by stiffness with variable sensitivity.

T cells are mechanosensitive but the effect of stiffness on their functions is still debated. We characterize herein how human primary CD4+ T cell functions are affected by stiffness within the physiological Young's modulus range of 0.5 kPa to 100 kPa. Stiffness modulates T lymphocyte migration and morphological changes induced by TCR/CD3 triggering. Stiffness also increases TCR-induced immune system, metabolism and cell-cycle-related genes. Yet, upon TCR/CD3 stimulation, while cytokine production increases within a wide range of stiffness, from hundreds of Pa to hundreds of kPa, T cell metabolic properties and cell cycle progression are only increased by the highest stiffness tested (100 kPa). Finally, mechanical properties of adherent antigen-presenting cells modulate cytokine production by T cells. Together, these results reveal that T cells discriminate between the wide range of stiffness values found in the body and adapt their responses accordingly.

Field evaporation behaviour for carbon nanotube thin-film

In recent years, the carbon nanotube (CNT) emitters used for ion sources or gas sensors have been investigated, and the progress of several approaches such as field ionization and field desorption sources has been reported. However, a major concern for these applications is possible loss of CNTs caused by field evaporation, which can shorten the lifetimes of CNT-based emitters used for high electric field ion sources. So in CNT-based field emitter technology, emitter lifetime and degradation will be key parameters to be controlled. However, up to now only very few investigations in this direction have been conducted. The reason for this might lie in the fact that one often considers that the threshold value of field evaporation for a kind of material ( 40 V/nm) is much higher than the field of ionization or desorption ( 10 V/nm) according to the metal material characteristics (such as the threshold values of field evaporation for tungsten and molybdenum are 54 V/nm and 45 V/nm, respectively). In this work, the carbon nanotube thin-film (the density of CNTs is about 2.5108/cm2) is fabricated by screen-printing method, and the field evaporation behavior of CNT thin-film is studied experimentally in an ultrahigh vacuum system typically operating at a pressure of lower than 10-9 Torr after a 4-hour bake-out at ~200℃. Unlike the vertically aligned CNT array having higher electric field around the edge of the array because of the shielding effect, the printed CNT thin-film has more uniform distribution of electric field and is very easy to relize the mass production. The results show that the prepared CNT thin-film has quite obvious field evaporation behavior (some contaminants have deposited on the surface of grid after field evaporation, and energy-dispersive X-ray spectroscopy elemental mapping result of the grid indicates that the contaminants consist mainly of carbon elements), with turn-on field in a range of 10.0-12.6 V/nm, ion current could reach up to hundreds of pA. Meanwhile, the results with scanning electron microscope analysis and field electron emission measurement indicate that the CNT distribution turns into more non-uniform distribution after field evaporation; even some CNTs are directly dragged away from the substrate by the strong field. The field evaporation of CNT thin-film also leads to field electron emission onset voltage increasing from 240 V to 300 V, field enhancement factor decreasing from 8300 to 4200, and threshold field of field evaporation rising from 10.0 V/nm to 12.6 V/nm. However, the repeatability of sample treated by the field evaporation brings about an improvement to a certain extent. It could be understood in this way: upon applying a positive voltage, the most protruding parts, which have the strongest emissive capability, are evaporated first, which leads to the declined field enhancement factor; the parts of CNTs which have relatively weak emissive capability are not evaporated. So the uniformity of electric field is improved through reducing the difference in field enhancement factor rather than surface morphology between carbon nanotubes. The field evaporation of CNT thin-film is also a process which improves the uniformity of electric field. Therefore, the stability and repeatability of the field electron emission for carbon nanotube thin-film are improved naturally.

An apparatus with a horizontal capillary tube intended for measurement of the surface tension of supercooled liquids

New experimental apparatus for measurement of the surface tension of liquids under the metastable supercooled state has been designed and assembled in the study. The measuring technique is similar to the method employed by P.T. Hacker [NACA TN 2510] in 1951. A short liquid thread of the liquid sample was sucked inside a horizontal capillary tube partly placed in a temperature-controlled glass chamber. One end of the capillary tube was connected to a setup with inert gas which allowed for precise tuning of the gas overpressure in order of hundreds of Pa. The open end of the capillary tube was precisely grinded and polished before the measurement in order to assure planarity and perpendicularity of the outer surface. The liquid meniscus at the open end was illuminated by a laser beam and observed by a digital camera. Application of an increasing overpressure of the inert gas at the inner meniscus of the liquid thread caused variation of the outer meniscus such that it gradually changed from concave to flat and subsequently convex shape. The surface tension at the temperature of the inner meniscus could be evaluated from the overpressure corresponding to exactly planar outer meniscus. Detailed description of the new setup together with results of the preliminary tests is provided in the study.

Characterization of Carbopol® hydrogel rheology for experimental tectonics and geodynamics

One of the long-standing challenges of modern tectonics and geodynamics is to fully understand the strong strain localization and its effects observed in the lithosphere, which presents viscous, as well as elastic and brittle properties. Recently yield stress–shear thinning hydrogels, such as Carbopol®, have been employed in analog modeling because of its great potential for mimicking the non-Newtonian behavior of rocks. Conversely its use has been limited by the difficulties in assessing its rheology and in preparing uniform samples. Ergo, it is essential to ensure a standard recipe, yielding to a reproducible behavior, no matter which rheometer model is used. We carried out, at four institutions (FAST, GFZ, IPGP and LET), a benchmark for developing a standard preparation and for testing the comparability of results. Then, we conducted a systematical rheological characterization of a wide range of Carbopol® formulas as a function of concentration, composition, pH, temperature and aging. Results show that neutral pH favors higher viscosity. The shear modulus, yield stress, viscosity, and shear thinning behavior increase with concentration. The linear viscoelastic range increases with concentration contrarily to what is observed in gelatins or colloidal suspensions. A weak inverse relationship between temperature and viscosity is found. Similarly, aging reduces both the viscosity and loss modulus, with reduction more evident for low concentration samples. Scaling analysis revealed that low concentration samples, i.e. <0.1wt.%, exhibiting shear thinning behavior and low yield stress, are appropriate to model the rising of thermal instabilities. Those at 0.5–1.0wt.%, showing yield stress in the order of hundreds of Pa and n ranging between 1.6 and 3.4 are good candidates to mimic the non-linear ductile behavior of crustal rocks. We conclude that tuning the visco-elasto-plastic rheology of Carbopol® would make this material a good candidate for modeling of also other geological processes.

Observation of a brine layer on an ice surface with an environmental scanning electron microscope at higher pressures and temperatures.

Observation of a uranyl-salt brine layer on an ice surface using backscattered electron detection and ice surface morphology using secondary-electron detection under equilibrium conditions was facilitated using an environmental scanning electron microscope (ESEM) at temperatures above 250 K and pressures of hundreds of Pa. The micrographs of a brine layer over ice grains prepared by either slow or shock freezing provided a complementary picture of the contaminated ice grain boundaries. Fluorescence spectroscopy of the uranyl ions in the brine layer confirmed that the species exists predominately in the solvated state under experimental conditions of ESEM.

Ratchets, red cells, and metastability.

Sickle cell disease is a genetic disorder in which a negatively charged glutamic acid is replaced by a hydrophobic valine on the surface of the hemoglobin molecule, leading to polymerization of the deoxygenated form, and resulting in microvascular obstruction. Because of the high volume occupancy under which polymerization occurs physiologically, this process has been an exemplar in the study of excluded volume effects on assembly. More recently, we have identified yet another type of crowding effect involving the obstruction of the ends at which the polymers grow as a consequence of the dense arrays in which these polymers form. This makes such solutions metastable, and leads to Brownian ratchet behavior in which pressure is exerted outward when the gel occupies a finite volume, as in an emulsion or red cell. Such behavior is capable of holding sickled cells in place in the microcirculation against weak pressure differentials (hundreds of Pa), but not against the typical pressures found in vivo.

Thermogravimetric method for a rapid estimation of vapor pressure and vaporization enthalpies of disubstituted benzoic acids: an attempt to correlate vapor pressures and vaporization enthalpies with structure

A rapid estimation of vapor pressure and vaporization enthalpies of some disubstituted benzoic acids (2,4-dihydroxybenzoic acid (2,4-DHBA), 2,6-dihydroxybenzoic acid (2,6-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), 2,4-dinitrobenzoic acid (2,4-DNBA), 3,4-dinitrobenzoic acid (3,4-DNBA), 2,5-dibromobenzoic acid (2,5-DBBA), and 3,5-dibromobenzoic acid (3,5-DBBA)) was made using a simultaneous TG/DSC apparatus operating with aluminum open crucibles under inert atmosphere in both isothermal and non-isothermal mode. No evidence of thermal decomposition (in the form of endo or exothermic effect) was found during each experiment. Vapor pressure was obtained in the range from some tenth to some hundreds of Pa after calibration with benzoic acid. All operative conditions (sample mass, temperature rage, and purge gas flow) were carefully checked in order to obtain reliable results. Internal consistency of the results obtained was checked by comparing the sublimation enthalpy obtained by the sum of the vaporization enthalpies derived by the global NITG and ITG data, the melting enthalpies from DSC adjusted at 298.15 using the molar isobaric heat capacities of both solid and liquid estimated according to a group additivity approach and that obtained from the sublimation enthalpies determined by torsion effusion corrected at 298.15 K using the same approach. Finally, some comments concerning the relationship between energetics and structure (substituent effect) are also reported.

Rapid neuronet inversion of 2D magnetotelluric data for monitoring of geoelectrical section parameters

The inverse MagnetoTelluric (MT) operator is approximated by means of the Neural Network (NN). The methodology of the NN interpretation in classes of the geoelectrical sections described by the hundreds of pa- rameters is proposed. Error of the NN inversion and field misfit are evaluated. A rapid NN algorithm solving the inverse problem and detecting changes of time-dependent dynamic parameters of the section is applied to 2D synthetic data.

Low temperature fast growth of nanocrystalline silicon films by rf-PECVD from SiH4/H2 gases: microstructural characterization

Hydrogenated nanocrystalline silicon thin films were deposited at a high rate of 0.8 nm s−1 by conventional (13.56 MHz) plasma enhanced chemical vapour deposition from SHi4/H2 gas mixture at a low temperature of 200 °C. The effects of hydrogen dilution, radio frequency power density, substrate temperature and deposition pressure on the crystalline volume fraction and the deposition rate of films were systematically investigated. The results show that the high hydrogen dilution and the substrate temperature are favourable for improving the crystallinity properties. The high deposition rate requires high power density over 0.7 W cm−2 in combination with high deposition pressure above several hundreds of Pa to overcome the degradation of film quality.

Production of highly charged ions in the range of energy of 10 V × q up to MeV

A new ion irradiation facility for the formation of beams of highly charged ions in a wide range of kinetic energy from about 10V×q up to MeV is presented. The ions are produced in sources of the Dresden EBIT type which allow the production of a wide spectrum of highly charged ions such as C6+, Ar18+, Ni28+, Kr35+ and Xe44+, respectively. The integral ion output of these ion sources is in the order of some μA per pulse at pulse widths of 2μs up to about 10μs. For individual ion charge states ion currents of up to about 100 nA per pulse can be obtained. In DC extraction mode (leaky mode) ion currents in the order of hundreds of pA are detected. An advanced Dresden EBIT type source, the Dresden EBIS-A, is employed at an irradiation facility. The target chamber comprises a sample manipulation and transfer system as well as numerous preparation and diagnostic tools. The facility will provide an experimental environment for basic research in atomic and solid state physics as well as for applied technology in areas such as surface engineering, surface analysis, nanostructuring and nanobiotechnology.

Transient response of a magneto-rheological suspension after a double-step shear strain

The mechanical response of a magneto-rheological suspension was monitored after the imposition of a double-step shear strain, consisting of a rapidly applied strain γ1, followed immediately by a second strain γ2, which was maintained for a long time, with the magnetic field held constant throughout. For 0.3<γ2/γ1<1, it was found that the shear stress would display significant fluctuations with typical magnitude of hundreds of Pa, and period of several hundred to thousands of seconds. A possible mechanism for this phenomenon may be the gradual rearrangement of the particle positions within the aggregates after the initial rapidly applied deformations.

Hollow cathode sputtering cluster source for low energy deposition: Deposition of Fe small clusters

We have developed a new cluster deposition source, which can be applied to the formation of nanostructured thin films. By our method, clusters are created by a hollow cathode sputtering at high pressure in the range of hundreds of Pa, which are directly deposited onto substrates. A pipe target with small internal diameter of 6 mm is used, and He is injected as a carrier gas while using Ar as a sputtering gas. The cluster size can be controlled between 2 and 6 nm in diameter, and high deposition rates up to 25 nm/min for 6 nm Fe clusters are obtained on a considerably wide substrate. It is also demonstrated that the deposition of 6 nm Fe clusters produces continuous films consisting of very small grains of nearly the same size with depositing clusters.

An adrenal slice preparation for the study of chromaffin cells and their cholinergic innervation

Thin slices (200–300 μm) of adrenal glands were prepared from Wistar rats. Patch-clamp recordings were made from visually identified chromaffin cells using the whole-cell and amphotericin B perforated-patch techniques. Electrophysiological properties of chromaffin cells in slices were similar to those in cultured cells. Catecholamine release from single chromaffin cells or cell clusters in slices was also measured by amperometry. Immunostaining of slices with an antineurofilament antibody revealed the presence of neuronal fibers. Acetylcholine release was stimulated either by raising external [K +] or by focally applying voltage pulses. Nicotinic excitatory postsynaptic currents (EPSCs) were detected, ranging from 20 pA to several hundreds of pA. Amplitude distributions of spontaneous EPSCs revealed clear equidistant peaks, supporting a quantal model for acetylcholine release onto chromaffin cells. The adrenal slice preparation therefore appears to be an excellent model for studying both the cholinergic innervation of chromaffin cells as well as catecholamine release from these cells.