Amethyst Technologies (United States)

In the abdominal segment of the human aorta under a patient's average resting conditions, pulsatile blood flow exhibits complex laminar patterns with secondary flows induced by adjacent branches and irregular vessel geometries. The flow dynamics becomes more complex when there is a pathological condition that causes changes in the normal structural composition of the vessel wall, for example, in the presence of an aneurysm. This work examines the hemodynamics of pulsatile blood flow in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and hemodynamic stresses in AAAs are performed in single-aneurysm, asymmetric, rigid wall models using the finite element method. We characterize pulsatile flow dynamics in AAAs for average resting conditions by means of identifying regions of disturbed flow and quantifying the disturbance by evaluating flow-induced stresses at the aneurysm wall, specifically wall pressure and wall shear stress. Physiologically realistic abdominal aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50 < or = Rem < or = 300, corresponding to a range of peak Reynolds numbers 262.5 < or = Repeak < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is depicted by a sequence of four different flow phases in one period of the cardiac pulse. Peak wall shear stress and peak wall pressure are reported as a function of the time-average Reynolds number and aneurysm asymmetry. The effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.

A method is presented for generating a beam with a beam shape that is independent of distance and frequency over large axial and frequency ranges. The half-width of the beam can be less than a wavelength at the low end of the frequency range and can hold this narrow waist for hundreds of wavelengths, giving a large depth of field. The phase fronts of this beam are planar and perpendicular to the beam axis over the depth of field. By virtue of the flat phase fronts and the frequency independence of the beam, a pulsed beam with flat pulse fronts and an unchanging time response can be created. This beam is shown to share some of the properties of an axicon. A numerical simulation is done to demonstrate the feasibility of generating such a beam with an annular array.

A concept of operations (CONOPS) for the Commercial and Business (CaB) aircraft synthetic vision systems (SVS) is described. The CaB SVS is expected to provide increased safety and operational benefits in normal and low visibility conditions. Providing operational benefits will promote SVS implementation in the Net, improve aviation safety, and assist in meeting the national aviation safety goal. SVS will enhance safety and enable consistent gate-to-gate aircraft operations in normal and low visibility conditions. The goal for developing SVS is to support operational minima as low as Category 3b in a variety of environments. For departure and ground operations, the SVS goal is to enable operations with a runway visual range of 300 feet. The system is an integrated display concept that provides a virtual visual environment. The SVS virtual visual environment is composed of three components: an enhanced intuitive view of the flight environment, hazard and obstacle defection and display, and precision navigation guidance. The virtual visual environment will support enhanced operations procedures during all phases of flight - ground operations, departure, en route, and arrival. The applications selected for emphasis in this document include low visibility departures and arrivals including parallel runway operations, and low visibility airport surface operations. These particular applications were selected because of significant potential benefits afforded by SVS.

Short-wave infrared barriode detectors were grown by molecular beam epitaxy. An absorption layer composition of In0.28Ga0.72As0.25Sb0.75 allowed for lattice matching to GaSb and cut-off wavelengths of 2.9 μm at 250 K and 3.0 μm at room temperature. Arrhenius plots of the dark current density showed diffusion limited dark currents approaching those expected for optimized HgCdTe-based detectors. Specific detectivity figures of around 7×1010 Jones and 1×1010 Jones were calculated, for 240 K and room temperature, respectively. Significantly, these devices could support focal plane arrays working at higher operating temperatures.

Despite the presence of over 56% Ni by weight, equiatomic NiTi is generally considered biocompatible as it naturally oxidises to form a surface oxide mainly composed of biocompatible oxides of titanium (TiOx). This layer is formed by an oxidation mechanism that promotes out-diffusion of Ti leaving a Ti-depleted, Ni rich subsurface. The long-term in vivo stability of the naturally grown TiOx layer has been a concern as Ni can leach out through this thin, defective layer. The leaching of nickel (Ni) is thus a continuing threat to the alloy’s otherwise outstanding biocompatibility. We have found that a layer of reactively sputtered tantalum (Ta) oxide on the bulk NiTi restricts Ti-out-migration through a biocompatible Ti/Ta inter-diffusion layer that provides a larger barrier against Ni leaching. We have investigated this inter-diffusion as a function of sputtering process parameters and post processing treatments. Surface and interface analytical techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, cross sectional transmission electron microscopy and non-destructive ion beam analysis techniques such as Rutherford backscattering spectrometry and particle induced X-ray emission were used to evaluate the nature of this inter-diffusion layer which can improve long-term biocompatibility of NiTi.

The capability of LIBS analysis of the cement raw material is improved by using a new spectrum standardization method.

We report the design, growth, processing, and characterization of resonant cavity enhanced photodiodes for the midwave infrared at ∼3.72 μm on GaSb. Using AlAsSb/GaSb mirrors, AlAsSb barrier and spacer layers and a thin 96 nm InAsSb absorber, we observed dark current and detectivity behavior superior to common InAsSb nBn detectors in the literature, with peak specific detectivity values of 8×1010 and 1×1010 cm Hz1/2 W−1 measured at 250 K and 300 K, respectively. In the same temperature range, the linewidth of the detector response was &amp;lt;44 nm and the quality factor ∼80. The peak quantum efficiency was &amp;gt;60% where the enhancement due to the resonant cavity was ∼20x. We estimate that the devices can operate close to, or slightly above, the background-limited infrared performance limit imposed on broadband detectors for a 300 K scene.

Two-operand binary addition is the most widely used arithmetic operation in modern datapath designs. To improve the efficiency of this operation, it is desirable to use an adder with good performance and area tradeoff characteristics. This paper presents an efficient carry-lookahead adder architecture based on the parallel-prefix computation graph. In our proposed method, we define the notion of triple-carry-operator, which computes the generate and propagate signals for a merged block which combines three adjacent blocks. We use this in conjunction with the classic approach of the carry-operator to compute the generate and propagate signals for a merged block combining two adjacent blocks. The timing-driven nature of the proposed design reduces the depth of the adder. In addition, we use a ripple-carry type of structure in the nontiming critical portion of the parallel-prefix computation network. These techniques help produce a good timing-area tradeoff characteristic. The experimental results indicate that our proposed adder is significantly faster than the popular Brent-Kung adder with some area overhead. On the adder hand, the proposed adder also shows marginally faster performance than the fast Kogge-Stone adder with significant area savings.

It has been shown that cocaine-induced convulsions and lethality appear to be mediated by serotonin and dopamine neurotransmission, respectively. However, many antidepressants considered for treatment of cocaine addiction target these monoamine systems and may thus amplify these toxic effects during relapse. In this study, the authors assessed whether pretreatment with antidepressants influences cocaine-induced toxicity in mice as well as the potency of these medications at cocaine-binding sites previously shown to be associated with cocaine toxicity. Overall, selective serotonin reuptake inhibitors (SSRIs) facilitated cocaine-induced convulsions but not lethality. Dopamine uptake inhibition facilitated cocaine-induced lethality, but not convulsion. The SSRI sertraline enhanced neither convulsions nor lethality and may be unique due to its high affinity for sigma receptors. These results have important implications for safe and effective addiction treatments.

Client questionnaires from 38 gender-specific substance abuse facilities throughout Ohio were analyzed to explore smoking prevalence, quit attempts, and readiness to quit cigarette use. The analysis revealed 79.7% of women used cigarettes at the time of the survey, 33.5% of current smokers had made at least one quit attempt within the past 12 months, and 55.2% of current smokers reported either contemplating or preparing to make a quit attempt. A multinomial logistic regression revealed that clients who experienced a past quit attempt were more likely to be in the contemplation and preparation stages and clients who smoked 30 out of the past 30 days were least likely to be in the preparation stage. Clients who reported smoking between 10-15 cigarettes a day were more likely to be in the contemplation stage than those who reported smoking <10 cigarettes a day. A three-pronged approach that examines the physiological, emotional, and social components of addiction is recommended.

Two important results desired in most powder-coating applications are: (1) a high first-pass transfer efficiency (FPTE); and (2) uniformity of the powder layer covering the surface to be coated. Both of these desired outcomes are influenced by the properties of powder and spraying process parameters involved in the electrostatic coating process. Many industries are unable to switch from solvent-based coatings to powder coatings because of the long color-change time required in industrial powder coating processes. An FPTE greater than 90% may eliminate the need for recycling of the overspray in some applications, thereby permitting fast color changes. To obtain a high FPTE and good appearance of a thin film, all relevant coating parameters must be optimized. In many powder-coating applications, particularly in aircraft coating, it is necessary to reduce film thickness to reduce the weight of the paint layer. However, the film must not have any surface defects and must have strong resistance against corrosion, UV radiation, and temperature fluctuations. Since surface defects can be caused by the presence of back corona during the electrostatic spraying process, it is often desirable to spray powder at high FPTE with minimal free ion current. To minimize ion current, it is possible to operate the corona gun at a lower voltage, such as -60 kV in place of -100 kV, with only minor reduction of FPTE but a threefold reduction of Q/M of the deposited powder. However, since most of the polymer powder acquires a bipolar charge distribution during the fluidization and transport processes, low-voltage corona discharge operations did not produce unipolar charge distribution during the spraying process. A bipolar charge distribution of the powder appears to produce dendritic clusters in the powder layer, resulting in a nonuniform film surface, as measured by an optical diffusive reflectance analyzer. The best film appearance was achieved with powder applied at -100 kV and cured slowly. It therefore appears that each application process must be optimized by both experimental studies and theoretical modeling to achieve the highest possible FPTE with minimal surface defects.

The extended-shortwave infrared wavelength range, encompassing wavelengths from 2.2 to 3 μm, is significantly underdeveloped when compared to the shortwave and midwave infrared bands. Achieving high performance detectors in the extended-shortwave range is desirable; however, it is unclear whether to approach the wavelength range via the detector structures and materials common to the shortwave regime or those common to the midwave regime. Both approaches are studied here. Electrical and optical characteristics of conventional photodiodes and nBn architecture detectors with 2.8 μm cutoff wavelengths are analyzed for detectors with both lattice-mismatched InGaAs and lattice-matched InGaAsSb absorbing regions. Regardless of the absorber material, the nBn detectors show nearly 3 orders of magnitude improvements in performance over the conventional photodiode architecture, and the lattice-matched InGaAsSb nBn exhibits a further reduction in the dark current by more than an order of magnitude when compared to the lattice-mismatched InGaAs nBn. The InGaAsSb nBn exhibits high quality optical detection resulting in a high performance detector in the extended-shortwave infrared band.

A novel taper-doping anode termination method is introduced for high-voltage silicon carbide devices. The method employs a subresolution two-tone termination mask to achieve a gray-scale exposure and a smoothly tapered photoresist profile. Using the tapered profile as an implantation mask, self-aligned 6-kV SiC PiN diodes are demonstrated with 90% of the parallel-plate breakdown voltage. The avalanche breakdown for the design is controlled and reversible. This one-step technique allows wide design control over the width and shape of the termination profile and has wide device and material applicability.

In this study, we verify the performance of the simultaneous equations method using an experimental active noise control system. The simultaneous equations method is based on a priciple different from the filtered-x algorithm requiring a filter modeled on a secondary path from a loudspeaker to an error microphone. Instead of the filter, called the secondary path filter, this method uses an auxiliary filter identifying the overall path consisting of a primary path, a noise control filter and the secondary path. As inferred from the configuration of the overall path, the auxiliary filter can provide two independent equations when two different coefficient vectors are given to the noise control filter. The method thereby estimates the coefficient vector of the noise control filter minimizing the output of the error microphone. In this paper, we propose the application of a frequency domain adaptive algorithm to the identification of the overall path. An improvement in the noise reduction speed is thereby expected. In this paper, we also present computer simulation results demonstrating that the simultaneous equations method can automatically recover the noise reduction effect degraded by path changes, and finally, using an experimental system, we indicate that the method successfully works in practical systems.

III-Sb barrier detectors suitable for the mid-wave infrared were grown on GaSb by molecular beam epitaxy. Using both bulk-InAsSb and an InAsSb–InAs strained layer superlattice, operation close to room temperature was demonstrated with cutoff wavelengths of 4.82 and 5.79 μm, respectively, with zero-bias operation possible for the bulk-InAsSb detector. X-ray diffraction, temperature dependent dark current, and spectral quantum efficiency were measured, and an analysis based on calculated specific detectivity was carried out. 1/f noise effects are considered. Results indicate that these optimized devices may be suitable as alternatives to InSb, or even HgCdTe, for many applications, especially where available power is limited.

A study of certain defects in GaInNAs, and their passivation. The passivation process could lead to more efficient photovoltaic devices.

InAs quantum-dot structures were grown using a GaAs1−xSbx matrix on a GaAs(001) substrate. The use of GaAs1−xSbx for the buffer and cap layers effectively suppressed coalescence between dots and significantly increased the dot density. The highest density (∼3.5 × 1011/cm2) was obtained for a nominal 3.0 monolayer deposition of InAs with an Sb composition of x = 13–14% in the GaAs1−xSbx matrix. When the Sb composition was increased to 18%, the resulting large photoluminescent red shift (∼90 meV) indicated the release of compressive strain inside the quantum dots. For x &amp;gt; 13%, we observed a significant decrease in photoluminescence intensity and an increase in the carrier lifetime (≥4.0 ns). This is attributed to the type-II band alignment between the quantum dots and matrix material.

In an earlier paper ["Theoretical Study of Molecular Contaminants on Silicon wafers: Interactions Between Molecular Contaminants and the Silicon Surface," Journal of the IEST, July/August 1998] a simple formulation was developed to describe interactions between gas phase molecules and solid surfaces. 1 Adsorption energies of various organic/inorganic molecules on silicon wafer surfaces were derived, In this paper, the relationship between the gas phase molecule concentration and the surface contamination density based on simple kinetic theories is established. The most important approximations in this derivation include the neglect of possible chemical reactions on the surface and the assumption that gas phase concentrations of pollutants are constants, both in time and in location. The mass transport mechanisms are ignored. With these approximations, the equilibrium in surface kinetics can be reached almost instantly for all the molecules investigated, even for those having activation energies as high as ∼ 72 kJ/mole. This agrees with the experimental data for moisture adsorption on stainless steel. 2 A guide is provided for material selection.

A general model is developed to characterize the effect of an ultrasonic measurement system on the experimental determination of ultrasonic scattering as a function of angle and frequency. The model includes arbitrary emitter beams and detector apertures as angular spectra of plane waves. Arbitrary emitted pulses and detector time gates are incorporated through frequency spectra of temporal harmonics. A transformation of variables is employed to express the spectrum of the measured pressure as a product in wave space of a system function and the Fourier transform of the medium variations. The mean-square value of the measured pressure spectrum is similarly expressed as a product of the squared magnitude of the system function and the power spectrum of the medium variations. The measured quantities are shown to become scaled values of intrinsic scattering characteristics when the system function weight is concentrated relative to the medium characteristics in wave space. The assumption of an indefinitely long detector gate is used to represent the system function as a product in which one factor is a beam function dependent on spatial frequency and the other factors are dependent on temporal frequency. Beam-function calculations as well as calculations of second moments and overall beam weight are made for identical Gaussian-shaped emitter and detector apertures to illustrate the blurring and weighting effects of measurement system beam patterns as a function of scattering angle. The moment calculations are shown to identify circumstances when the medium variation function can be factored out from under the integral and the measurement represented as a simple product of the medium properties and a measurement system weight. The results may be used to design scattering experiments in which degradations due to system effects are within acceptable limits.

Two types of InSb structures, epilayers and quantum wells (QWs), have been grown on on-axis and 6°-off-axis Ge (001) substrates and examined by reflection high-energy electron diffraction, transmission electron microscopy, X-ray diffraction, atomic force microscopy, and the van der Pauw and Hall effect techniques. Anti-phase domain defects, which prevail in these InSb structures when grown on on-axis Ge (001) substrates, are significantly decreased by the use of 6° off-axis Ge (001) substrates. Such off-axis substrates also lead to reductions in the densities of micro-twins and threading dislocations. Room-temperature electron mobilities in 4.0-μm-thick InSb epilayers and 25-nm-thick InSb QWs grown on 6°-off-axis Ge (001) substrates are 59 000 and 14 000 cm2/(V s), respectively, which are ∼1.5 times higher than their counterparts grown on on-axis Ge (001) substrates. These improved mobilities are the highest among the reported values for each type of structure grown on Ge (001) substrates.