Modeling of ground motion from a 1994 Northridge aftershock using a tomographic velocity model of the Los Angeles Basin

The 1994 Northridge mainshock and its aftershocks show a complex pattern of peak accelerations at stations located in the Los Angeles Basin. The waveforms contain multiples of body-wave phases and extensive surface waves at frequencies mostly below 1 Hz. In particular, for stations at distances greater than 18 km, secondary arrivals show larger accelerations than the direct S-wave arrivals. The mainshock waveforms are further complicated by irregularities of the source rupture. We use 2D finite difference to evaluate the effect of lateral variations in seismic velocity on the amplitude of shear-wave energy and to distinguish the effects of source and propagation path. We model waveforms from one aftershock recorded at nine stations deployed along a 60-km-long profile extending into the Los Angeles Basin. We use a two-dimensional slice through the 3D tomography model of the Los Angeles Basin in the 2D finite-difference calculations. These synthetic waveforms fit the aftershock waveforms significantly better than corresponding waveforms determined from simple 1D velocity models. With the addition of a thin low-velocity surface layer above the tomography model, the finite-difference synthetics reproduce most of the important features of the recorded data, in particular, the large-amplitude arrivals 7 to 10 sec following the direct S arrival. These arrivals correspond to the SS arrival, which is sharply refracted at the basin edge, and the S-wave with multiple legs trapped by the dipping near surface gradient. For large earthquakes located either inside or outside the basin, these phases can be the cause of the largest and hence potentially most hazardous shaking in the Los Angeles Basin

Ultrasound-guided percutaneous delivery of tissue-engineered endothelial cells to the adventitia of stented arteries controls the response to vascular injury in a porcine model

Objective High restenosis rates are a limitation of peripheral vascular interventions. Previous studies have shown that surgical implantation of a tissue-engineered endothelium onto the adventitia surface of injured vessels regulates vascular repair. In the present study, we developed a particulate formulation of tissue-engineered endothelium and a method to deliver the formulation perivascular to injured blood vessels using a percutaneous, minimally invasive technique. Methods Stainless steel stents were implanted in 18 balloon-injured femoral arteries of nine domestic swine, followed by ultrasound-guided percutaneous perivascular injection of gelatin particles containing cultured allogeneic porcine aortic endothelial cells (PAE). Controls received injections of empty particles (matrix) or no perivascular injection (sham) after stent deployment. Animals were sacrificed after 90 days. Results Angiographic analysis revealed a significantly greater lumen diameter in the stented segments of arteries treated with PAE/matrix (4.72 ± 0.12 mm) compared with matrix (4.01 ± 0.20 mm) or sham (4.03 ± 0.16 mm) controls (P < .05). Similarly, histologic analysis revealed that PAE/matrix-treated arteries had the greatest lumen area (20.4 ± 0.7 mm[superscript 2]; P < .05) compared with controls (16.1 ± 0.9 mm[superscript 2] and 17.1 ± 1.0 mm[superscript 2] for sham and matrix controls, respectively) and the smallest intimal area (3.3 ± 0.4 mm[superscript 2]; P < .05) compared with controls (6.2 ± 0.5 mm[superscript 2] and 4.4 ± 0.5 mm[superscript 2] for sham and matrix controls, respectively). Overall, PAE-treated arteries had a 33% to 50% decrease in percent occlusion (P < .05) compared with controls. Histopathological analysis revealed fewer leukocytes present in the intima in the PAE/matrix group compared with control groups, suggesting that the biological effects were in part due to inhibition of the inflammatory phase of the vascular response to injury. Conclusions Minimally invasive, perivascular delivery of PAE/matrix to stented arteries was performed safely using ultrasound-guided percutaneous injections and significantly decreased stenosis. Application at the time of or subsequent to peripheral interventions may decrease clinical restenosis rates

Tuning adhesion failure strength for tissue-specific applications

Soft tissue adhesives are employed to repair and seal many different organs, which range in both tissue surface chemistry and mechanical challenges during organ function. This complexity motivates the development of tunable adhesive materials with high resistance to uniaxial or multiaxial loads dictated by a specific organ environment. Co-polymeric hydrogels comprising aminated star polyethylene glycol and dextran aldehyde (PEG:dextran) are materials exhibiting physico-chemical properties that can be modified to achieve this organ- and tissue-specific adhesion performance. Here we report that resistance to failure under specific loading conditions, as well as tissue response at the adhesive material–tissue interface, can be modulated through regulation of the number and density of adhesive aldehyde groups. We find that atomic force microscopy (AFM) can characterize the material aldehyde density available for tissue interaction, and in this way enable rapid, informed material choice. Further, the correlation between AFM quantification of nanoscale unbinding forces with macroscale measurements of adhesion strength by uniaxial tension or multiaxial burst pressure allows the design of materials with specific cohesion and adhesion strengths. However, failure strength alone does not predict optimal in vivo reactivity. Thus, we demonstrate that the development of adhesive materials is significantly enabled when experiments are integrated along length scales to consider organ chemistry and mechanical loading states concurrently with adhesive material properties and tissue response.National Science Foundation (U.S.) (Career Award)American Society for Engineering Education. National Defense Science and Engineering Graduate FellowshipNational Institutes of Health (U.S.) (Grant ERE GM 49039

Automated Translation and Accelerated Solving of Differential Equations on Multiple GPU Platforms

We demonstrate a high-performance vendor-agnostic method for massively parallel solving of ensembles of ordinary differential equations (ODEs) and stochastic differential equations (SDEs) on GPUs. The method is integrated with a widely used differential equation solver library in a high-level language (Julia's DifferentialEquations.jl) and enables GPU acceleration without requiring code changes by the user. Our approach achieves state-of-the-art performance compared to hand-optimized CUDA-C++ kernels, while performing $20-100\times$ faster than the vectorized-map (\texttt{vmap}) approach implemented in JAX and PyTorch. Performance evaluation on NVIDIA, AMD, Intel, and Apple GPUs demonstrates performance portability and vendor-agnosticism. We show composability with MPI to enable distributed multi-GPU workflows. The implemented solvers are fully featured, supporting event handling, automatic differentiation, and incorporating of datasets via the GPU's texture memory, allowing scientists to take advantage of GPU acceleration on all major current architectures without changing their model code and without loss of performance.Comment: 11 figure

Reply to Ruan et al. (2017): Non-medical use of prescription opioids is associated with heroin initiation among US veterans.

We thank Ruan and colleagues for their letter and appreciate their comments regarding our recent study, which demonstrated an independent association between non-medical use of prescription opioids (NMUPO) and heroin initiation among US veterans

Non-medical use of prescription opioids is associated with heroin initiation among US veterans: a prospective cohort study

Aims: To estimate the influence of non-medical use of prescription opioids (NMUPO) on heroin initiation among US veterans receiving medical care. Design: Using a multivariable Cox regression model, we analyzed data from a prospective, multi-site, observational study of HIV-infected and an age/race/site-matched control group of HIV-uninfected veterans in care in the United States. Approximately annual behavioral assessments were conducted and contained self-reported measures of NMUPO and heroin use. Setting: Veterans Health Administration (VHA) infectious disease and primary care clinics in Atlanta, Baltimore, New York, Houston, Los Angeles, Pittsburgh and Washington, DC. Participants: A total of 3396 HIV-infected and uninfected patients enrolled into the Veterans Aging Cohort Study who reported no life-time NMUPO or heroin use, had no opioid use disorder diagnoses at baseline and who were followed between 2002 and 2012. Measurements: The primary outcome measure was self-reported incident heroin use and the primary exposure of interest was new-onset NMUPO. Our final model was adjusted for socio-demographics, pain interference, prior diagnoses of post-traumatic stress disorder and/or depression and self-reported other substance use. Findings: Using a multivariable Cox regression model, we found that non-medical use of prescription opioids NMUPO was associated positively and independently with heroin initiation [adjusted hazard ratio (AHR) = 5.43, 95% confidence interval (CI) = 4.01, 7.35]. Conclusions: New-onset non-medical use of prescription opioids (NMUPO) is a strong risk factor for heroin initiation among HIV-infected and uninfected veterans in the United States who reported no previous history of NMUPO or illicit opioid use