48 Background. Nucleic acid amplification tests (NAATs) are the primary means of 49 identifying acute infections caused by severe acute respiratory syndrome coronavirus 2 50 (SARS-CoV-2). Accurate and fast test results may permit more efficient use of protective and 51 isolation resources and allow for rapid therapeutic interventions. 52 Methods. We evaluated the analytical and clinical performance characteristics of the Xpert ® 53 Xpress SARS-CoV-2 (Xpert) test, a rapid, automated molecular test for SARS-CoV-2. 54 Analytical sensitivity and specificity/interference were assessed with infectious SARS-CoV-2, 55 other infectious coronavirus species including SARS-CoV, and 85 nasopharyngeal swab 56 specimens positive for other respiratory viruses including endemic human coronaviruses 57 (hCoVs). Clinical performance was assessed using 483 remnant upper and lower respiratory 58 specimens previously analyzed by standard of care (SOC) NAATs. 59 Results. The limit of detection of the Xpert test was 0.01 plaque forming units (PFU)/mL. 60 Other hCoVs, including Middle East Respiratory Syndrome coronavirus, were not detected by 61 the Xpert test. SARS-CoV, a closely related species in the Sarbecovirus subgenus, was 62 detected by a broad-range target (E) but was distinguished from SARS-CoV-2 (SARS-CoV-2-63 specific N2 target). Compared to SOC NAATs, the positive agreement of the Xpert test was 64 219/220 (99.5%) and the negative agreement was 250/261 (95.8%). A third tie-breaker 65 NAAT resolved all but three of the discordant results in favor the Xpert test. 66 Conclusions. The Xpert test provided sensitive and accurate detection of SARS-CoV-2 in a 67 variety of upper and lower respiratory tract specimens. The high sensitivity and fast time to 68 results of approximately 45 minutes may impact patient management. 69 70 Laboratory diagnosis of infections caused by severe acute respiratory syndrome coronavirus 2 72 (SARS-CoV-2) is usually accomplished by performing nucleic acid amplification tests 73 (NAATs) on respiratory tract specimens. An antibody response is often not detected in the 74 first week to ten days of symptoms and antibody testing is therefore generally unhelpful for 75 acute diagnosis(1-3), with virus isolation in culture presenting significant biosafety risks. 76 Upper respiratory tract (URT) specimens such as nasopharyngeal swabs (NPS) and 77 oropharyngeal swabs (OPS) generally have high SARS-CoV-2 viral loads upon symptom 78 onset.(2, 4-6) URT specimens may also have detectable RNA during the pre-symptomatic 79 period(7), and pediatric patients who remain asymptomatic through the entire course of 80 on June 9, 2020 by guest http://jcm.asm.org/ Downloaded from 4 infection can persistently shed RNA in URT specimens for two weeks or longer.(4, 8) 81 Importantly, NPS may have higher viral loads than OPS.(6) Lower respiratory tract (LRT) 82 specimens including sputum(7, 9) and tracheal aspirates(10) (TA) are often positive for RNA 83 early in disease and remain positive longer than URT sources.(5) 84 NAATs are...
The stimuli-sensitive hydrogel is an injectable formulation that is used to deliver drugs, cells, and genes into the body. Hydrogels are available in various physical forms such as solid molded, pressed powder matrix, microparticle, coating, or membrane forms. The network structure of hydrogels can be macroporous, microporous, or nonporous. Different categories of biomaterials, such as natural, synthetic, and combinations (e.g., semisynthetic such as natural-natural, natural-synthetic, and synthetic-synthetic polymers), are commonly used in hydrogel preparation. Classification of hydrogels mainly depends upon physical stimuli (temperature, electric fields, solvent composition, light, pressure, sound, and magnetic fields) and chemical or biochemical stimuli (pH, ions, and specific molecular recognition events). Several approaches for the synthesis of hydrogels have been reported, including emulsification, micromolding, photolithography, isostatic ultra high pressure, and microfluidic techniques. Hydrogels provide structural integrity and cellular organization, serve as tissue barriers, act as bioadhesive and drug depots, deliver bioactive agents and cells, and possess unique swelling properties and structures. This review provides a detailed account of the need for development of hydrogels, along with the materials used and techniques adopted to manufacture scaffolds for tissue engineering and for prolonged drug, cell, and gene delivery.
We study the most practical problem setup for evaluating adversarial robustness of a machine learning system with limited access: the hard-label black-box attack setting for generating adversarial examples, where limited model queries are allowed and only the decision is provided to a queried data input. Several algorithms have been proposed for this problem but they typically require huge amount (>20,000) of queries for attacking one example. Among them, one of the state-of-the-art approaches showed that hard-label attack can be modeled as an optimization problem where the objective function can be evaluated by binary search with additional model queries, thereby a zeroth order optimization algorithm can be applied. In this paper, we adopt the same optimization formulation but propose to directly estimate the sign of gradient at any direction instead of the gradient itself, which enjoys the benefit of single query. Using this single query oracle for retrieving sign of directional derivative, we develop a novel query-efficient Sign-OPT approach for hard-label black-box attack. We provide a convergence analysis of the new algorithm and conduct experiments on several models on MNIST, CIFAR-10 and ImageNet. We find that Sign-OPT attack consistently requires 5× to 10× fewer queries when compared to the current state-of-the-art approaches, and usually converges to an adversarial example with smaller perturbation.
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