330 research outputs found
Shear stress activation of nitric oxide synthase and increased NO levels in human red blood cells
Since the discovery of nitric oxide (NO) as a vasoactive molecule, red blood cells (RBC) have been considered to participate in NO-mediated control of the circulation. The classical role attributed to RBC was scavenging of NO, thereby impacting the local bioavailability of this important regulator of vascular tone^1^. RBC have been shown to be a source of NO, primarily via its transport bound to haemoglobin^2, 3^. Under specific conditions, haemoglobin plays an active role in converting NO derivatives (e.g., nitrite) to NO^4, 5^, with this NO originating from RBC being an effective modulator of vascular smooth muscle tone^6^. Interestingly, RBC contain a NO synthase (NOS) protein^7^, can actively synthesize NO using L-arginine as a substrate^8^, and can export NO under appropriate conditions^8, 9^. It has been previously hypothesized that RBC NOS may be activated by shear forces acting on the cell^10^, and we have recently shown that RBC NOS phosphorylation can be enhanced by subjecting RBC in suspension to shearing forces^9^: NO concentration in the suspending medium was increased subsequent to flow of RBC suspensions through five [mu]m pores^11^. We have now directly demonstrated increased RBC NOS activity and intracellular NO levels in immobilized RBC exposed to well-defined fluid shear stress. Immunostaining for serine 1177 phosphorylation and the NO-sensitive fluorescent probe diaminofluorescein were employed. Our results suggest that RBC deformation in constricted vessels may increase NO levels and favor vasodilation, thereby providing an important role for RBC in regulating the circulation
Graphics processing unit accelerated computation of digital holograms
Cataloged from PDF version of article.An approximation for fast digital hologram generation is implemented on a central processing unit (CPU), a graphics processing unit (GPU), and a multi-GPU computational platform. The computational performance of the method on each platform is measured and compared. The computational speed on the GPU platform is much faster than on a CPU, and the algorithm could be further accelerated on a multi-GPU platform. In addition, the accuracy of the algorithm for single-and double-precision arithmetic is evaluated. The quality of the reconstruction from the algorithm using single-precision arithmetic is comparable with the quality from the double-precision arithmetic, and thus the implementation using single-precision arithmetic on a multi-GPU platform can be used for holographic video displays. (C) 2009 Optical Society of America
Digital Holographic Three-Dimensional Video Displays
Cataloged from PDF version of article.Holography aims to record and regenerate volume
filling light fields to reproduce ghost-like 3-D images that are
optically indistinguishable from their physical 3-D originals.
Digital holographic video displays are pixelated devices on which
digital holograms can be written at video rates. Spatial light
modulators (SLMs) are used for such purposes in practice; even
though it is desirable to have SLMs that can modulate both the
phase and amplitude of the incident light at each pixel, usually
amplitude-only or phase-only SLMs are available. Many laboratories
have reported working prototypes using different designs.
Size and resolution of the SLMs are quite demanding for
satisfactory 3-D reconstructions. Space–bandwidth product
(SBP) seems like a good metric for quality analysis. Even though
moderate SBP is satisfactory for a stationary observer with no
lateral or rotational motion, the required SBP quickly increases
when such motion is allowed. Multi-SLM designs, especially over
curved surfaces, relieve high bandwidth requirements, and
therefore, are strong candidates for futuristic holographic video
displays. Holograms are quite robust to noise and quantization. It
is demonstrated that either laser or light-emitting diode (LED)
illumination is feasible. Current research momentum is increasing
with many exciting and encouraging results
Circular holographic video display system
Cataloged from PDF version of article.A circular holographic video display system reconstructs
holographic video. Phase-only spatial light modulators are tiled in a circular
configuration in order to increase the field of view. A beam-splitter is used
to align the active area of the SLMs side by side without any gap. With the
help of this configuration observers can see 3D ghost-like image floating in
space and can move and rotate around the object. The 3D reconstructions can be observed binocularly. Experimental results are satisfactory. © 2011 Optical Society of Americ
Real-time phase-only color holographic video display system using LED illumination
Cataloged from PDF version of article.A real-time full-color phase-only holographic display system generates holograms of 3D objects. The system includes a 3D object formed by voxels, an internet-based transmission capability that transmits the object information to the server, a real-time hologram generation unit, and a holographic display unit with incoherent illumination. The server calculates three phase holograms for RGB components using multiple GPUs. The resultant phase holograms are saved into an RGB bitmap image and loaded to the phase-only spatial light modulators (SLMs). SLMs are illuminated uniformly by LEDs, and reconstructed waves are aligned and overlapped by using high precision optics and stages. Experimental results are satisfactory. © 2009 Optical Society of America
A Preliminary Technique for the Isolation and Culture of Brown Trout (Salmo trutta macrostigma, Dumeril, 1858) Spermatogonial Stem Cell
This study was aimed to find a practical technique for isolation and culture spermatogonial stem cells from male brown trout (Salmo trutta macrostigma). Twelve wild juvenile male were obtained from Kılıç Trout Fish Farm (Kahramanmaraş, Turkey). The juveniles were taken alive to the aquaria unit and stored in a 1000-liter capacity fiberglass tank. In order to identify the best size, age and testis structure of S.t. macrostigma for spermatogonial stem cell isolation and culture. Morphological and histological testis conditions were assessed. Fish were anesthetized with 0.04% 2-phenoxethanol. The surface of the fish was sterilized with 70% ethanol. Twelve fish were divided into two groups for enzyme digestion, and each group was divided into two replicates (three fish per replicate). Testis tissue of group one were digested by 0.25% trypsin- EDTA, and testis tissues of group two were digested by 0.05% trypsin-EDTA. At the end of the trial, first, the best age, size and weight of the male fish for spermatogonial stem cell isolation and culture were identified as 5+ month old, 12.13±1.5 cm, 19, 25±7.05 g respectively. Then, the highest spermatogonial stem cells were measured in the stage one and two of the testes. Finally, isolation and culture conditions were optimized for male S.t. macrostigma. Spermatogonial stem cell isolation and culture techniques were defined for fish in order to be used in surrogate reproduction technologies and gene transfer systems
A Kinetic Model for Chelating Extraction of Metals from Spent Hydrodesulphurization Catalyst by Complexing Agent
In this present paper, chelating extraction of metals from spent hydrodesulphurization catalyst was carried out using ethylene diamine tetraacetic acid as complexing agent. Mo, Ni and Co metals were precipitated in ammonium molybdate, nickel dimethylglyoxime and cobalt hydroxide forms at pH:2, pH:6 and pH:10, respectively. The highest metal extraction yields (90.22% Mo, 96.71% Co, 95.31% Ni and 19.98% Al) were achieved under optimum process conditions. The activation energy values (Ea) of Co, Mo and Ni were calculated as 14.36 kJ/mol, 16.85 kJ/mol and 15.93 kJ/mol, respectively. It was determined that leaching kinetics fitted to the pseudo-first homogenous model and the chelating process was controlled by diffusion mechanism. In the light of the kinetic data, the kinetic equation including the process parameters was obtained as follows: ln(1-x)=1.217×10-4[(CA)1.068(D)-0.929(K/S)-0.850(R)0.185exp(-6462.6/T)]t. The results provided a new approach both for reducing the solid waste load of the petrochemical industry and for efficient recovery of metals from the spent hydrodesulphurization catalyst using EDTA. © 2020, The Indian Institute of Metals - IIM
'ACOUSTO-OPTIC SENSING FOR SAFE MRI PROCEDURES'
In this work, a novel sensor platform is developed for safer and more effective magnetic resonance imaging (MRI). This is achieved by tracking interventional devices, such as guidewires and catheters during interventional MRI procedures, and by measuring the radio frequency (RF) field to assess RF safety of patients with implants, such as pacemakers, during diagnostic MRI. The sensor is based on an acousto-optic modulator coupled with a miniature antenna. This structure is realized on an optical fiber which is immune to the RF field and eliminates the need for conducting lines. The acousto-optic modulator consists of a piezo-electric transducer and a fiber Bragg grating (FBG). The piezoelectric transducer is electrically connected to the miniature antenna and mechanically coupled to the FBG. Local RF signal received by the miniature antenna is converted to acoustic waves by the piezoelectric transducer. Acoustic waves change the grating geometry on the FBG, thus the reflected light from the FBG is modulated. For diagnostic imaging, short dipole antennas are used for sensing the local electric field, which is the primary cause of RF induced heating. For tracking purposes, small loop antennas are used for capturing local MRI signal which contains the location information. In this thesis, a comprehensive model for the acousto-optic modulator is developed and validated through sensitivity and linearity tests. Prototype RF field sensors are built and characterized: sensitivity of 1.36mV/nT and 98 μV/V/m with minimum detectable field strength of 8.2pT/√Hz and 2.7V/m/√Hz and dynamic range of 117dB/√Hz at 23MHz are achieved with 4mm single loop and 8mm short dipole antennas, respectively. These figures are competitive with commercial sensors with much larger form factors. Catheter tracking capability of the sensor under MRI is demonstrated in-vivo in swine in a 0.55T scanner using an 8F catheter in addition to phantom studies under 0.55T and 1.5T clinical MRI systems.Ph.D
Neural Collapse with Normalized Features: A Geometric Analysis over the Riemannian Manifold
When training overparameterized deep networks for classification tasks, it
has been widely observed that the learned features exhibit a so-called "neural
collapse" phenomenon. More specifically, for the output features of the
penultimate layer, for each class the within-class features converge to their
means, and the means of different classes exhibit a certain tight frame
structure, which is also aligned with the last layer's classifier. As feature
normalization in the last layer becomes a common practice in modern
representation learning, in this work we theoretically justify the neural
collapse phenomenon for normalized features. Based on an unconstrained feature
model, we simplify the empirical loss function in a multi-class classification
task into a nonconvex optimization problem over the Riemannian manifold by
constraining all features and classifiers over the sphere. In this context, we
analyze the nonconvex landscape of the Riemannian optimization problem over the
product of spheres, showing a benign global landscape in the sense that the
only global minimizers are the neural collapse solutions while all other
critical points are strict saddles with negative curvature. Experimental
results on practical deep networks corroborate our theory and demonstrate that
better representations can be learned faster via feature normalization.Comment: The first two authors contributed to this work equally; 38 pages, 13
figures. Accepted at NeurIPS'2
Randomized Histogram Matching: A Simple Augmentation for Unsupervised Domain Adaptation in Overhead Imagery
Modern deep neural networks (DNNs) are highly accurate on many recognition
tasks for overhead (e.g., satellite) imagery. However, visual domain shifts
(e.g., statistical changes due to geography, sensor, or atmospheric conditions)
remain a challenge, causing the accuracy of DNNs to degrade substantially and
unpredictably when testing on new sets of imagery. In this work, we model
domain shifts caused by variations in imaging hardware, lighting, and other
conditions as non-linear pixel-wise transformations, and we perform a
systematic study indicating that modern DNNs can become largely robust to these
types of transformations, if provided with appropriate training data
augmentation. In general, however, we do not know the transformation between
two sets of imagery. To overcome this, we propose a fast real-time unsupervised
training augmentation technique, termed randomized histogram matching (RHM). We
conduct experiments with two large benchmark datasets for building segmentation
and find that despite its simplicity, RHM consistently yields similar or
superior performance compared to state-of-the-art unsupervised domain
adaptation approaches, while being significantly simpler and more
computationally efficient. RHM also offers substantially better performance
than other comparably simple approaches that are widely used for overhead
imagery.Comment: Includes a main paper (10 pages). This paper is currently undergoing
peer revie
- …