The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors

We present low temperature electrical transport experiments in five field effect transistor devices consisting of monolayer, bilayer and trilayer MoS2 films, mechanically exfoliated onto Si/SiO2 substrate. Our experiments reveal that the electronic states in all films are localized well up to the room temperature over the experimentally accessible range of gate voltage. This manifests in two dimensional (2D) variable range hopping (VRH) at high temperatures, while below \sim 30 K the conductivity displays oscillatory structures in gate voltage arising from resonant tunneling at the localized sites. From the correlation energy (T0) of VRH and gate voltage dependence of conductivity, we suggest that Coulomb potential from trapped charges in the substrate are the dominant source of disorder in MoS2 field effect devices, which leads to carrier localization as well.Comment: 10 pages, 5 figures; ACS Nano (2011

Multicountry Prospective Clinical Evaluation of Two Enzyme-Linked Immunosorbent Assays and Two Rapid Diagnostic Tests for Diagnosing Dengue Fever

We evaluated four dengue diagnostic devices from Alere, including the SD Bioline Dengue Duo (nonstructural [NS] 1 Ag and IgG/IgM), the Panbio Dengue Duo Cassette (IgM/IgG) rapid diagnostic tests (RDTs), and the Panbio dengue IgM and IgG capture enzyme-linked immunosorbent assays (ELISAs) in a prospective, controlled, multicenter study in Peru, Venezuela, Cambodia, and the United States, using samples from 1,021 febrile individuals. Archived, well-characterized samples from an additional 135 febrile individuals from Thailand were also used. Reference testing was performed on all samples using an algorithm involving virus isolation, in-house IgM and IgG capture ELISAs, and plaque reduction neutralization tests (PRNT) to determine the infection status of the individual. The primary endpoints were the clinical sensitivities and specificities of these devices. The SD Bioline Dengue Duo had an overall sensitivity of 87.3% (95% confidence interval [CI], 84.1 to 90.2%) and specificity of 86.8% (95% CI, 83.9 to 89.3%) during the first 14 days post-symptom onset (p.s.o.). The Panbio Dengue Duo Cassette demonstrated a sensitivity of 92.1% (87.8 to 95.2%) and specificity of 62.2% (54.5 to 69.5%) during days 4 to 14 p.s.o. The Panbio IgM capture ELISA had a sensitivity of 87.6% (82.7 to 91.4%) and specificity of 88.1% (82.2 to 92.6%) during days 4 to 14 p.s.o. Finally, the Panbio IgG capture ELISA had a sensitivity of 69.6% (62.1 to 76.4%) and a specificity of 88.4% (82.6 to 92.8%) during days 4 to 14 p.s.o. for identification of secondary dengue infections. This multicountry prospective study resulted in reliable real-world performance data that will facilitate data-driven laboratory test choices for managing patient care during dengue outbreaks

Role of NF-KappaB/REL proteins in mediating innate immune responses in Drosophila melanogaster

In order to survive, the fruit fly Drosophila melanogaster needs to have a robust immune system to protect itself from numerous pathogenic microorganisms that are ubiquitous in its natural habitat. In two related projects, we studied the role of Rel transcription factors in mediating these immune responses. There are three Rel transcription factors, closely related to mammalian NF-KappaB: Dorsal, Dif, and Relish. They play an important role in mounting aspects of this response, including the inducible expression of antimicrobial peptides. To study the roles of these transcription factors in vivo, we used microarrays to determine the effect of null mutations in individual transcription factors on larval immune gene expression. Of the 188 genes that were significantly up-regulated in wildtype larvae upon bacterial challenge, overlapping but distinct groups of genes were affected in the Rel mutants. We also ectopically expressed Dorsal or Dif and used cDNA microarrays to determine the genes that were up-regulated in the presence of these transcription factors. Combining this data, we also identified novel genes that may be specific targets of Dif. In a related project, we observed that injection of a fungal secondary metabolite, Destruxin A reduced expression of various antimicrobial peptide genes. This reduction appeared to be mediated through suppression of the IMD pathway, through Relish. Destruxins are a class of cyclic depsipeptides produced by various fungi including the entomopathogen Metarhizium anisopliae. Though a direct relationship has been established between Destruxin production and fungal virulence, their in vivo mode of action during pathogenesis remained largely uncharacterized. To explore these effects, we looked at changes in gene expression following injection of Destruxin A into Drosophila. Microarray results revealed reduced expression of various AMPs that play a major role in the fly's humoral immune response. Flies co-injected with Destruxin A and the Gram-negative bacteria E.coli, showed increased mortality and an accompanying increase in bacterial titers. This mortality was rescued through ectopic activation of IMD pathway components upstream of Relish that are responsible for AMP induction. Together, these results suggest a novel role for Destruxin A in specific suppression of the humoral immune response in insects

An Approach to Improving Test Powers in Cox Proportional Hazards Models

In power analysis for significance test of the treatment variable in the multivariable Cox proportional hazards models, the variance of the estimated log-hazard ratio for the treatment effect is usually approximated by inverting the expected null information matrix. Because in many typical power analysis settings, assumed true values of the hazard ratios are not necessarily close to one, the accuracy of inverting the expected null is not theoretically guaranteed. A null variance in power calculations underestimates or overestimates the true variance in different treatment allocation settings when the treatment allocation ratio is far from one, similarly alternative variance in power calculations predicts inaccurate results in different treatment allocation settings. When the study events are rare, the alternative variance predicts accurate results in predicting the power, but the alternative variance does not provide accurate results when the study events are not rare. To address this problem, we propose an approach to estimating the variance, and this approach is compared with three widely used approaches in practice. The null variance in power calculations can be replaced with the proposed adjusted alternative variance derived under the assumed true value of the hazard ratio for the treatment effect. This approach is explored theoretically and by the simulations in this research. In this approach, we improve the variance of the log hazard ratio for the treatment effect and compare it with the traditional null variance, the traditional alternative variance, and another variance using log-rank test under proportional hazard alternatives. The most accurate expression of the variance has a relatively simple form. The variance is scaled up by a variance inflation factor, denoted by $VIF$. Our simulations for the relative bias of standard error and the power of the test for the treatment effect under the proposed variance are compared to the other standard variances. The results provide evidence that our proposed variance is a better estimator for the true variance of the log hazard ratio for the treatment effect under the study. Furthermore, one application with real-life examples is illustrated to evaluate the effectiveness of the proposed variance

Microscopic Mechanism of 1/f Noise in Graphene: Role of Energy Band Dispersion

A distinctive feature of single-layer graphene is the linearly dispersive energy bands, which in the case of multilayer graphene become parabolic. A simple electrical transport-based probe to differentiate between these two band structures will be immensely valuable, particularly when quantum Hall measurements are difficult, such as in chemically synthesized graphene nanoribbons. Here we show that the flicker noise, or the 1/f noise, in electrical resistance is a sensitive and robust probe to the band structure of graphene. At low temperatures, the dependence of noise magnitude on the carrier density was found to be opposite for the linear and parabolic bands. We explain our data with a comprehensive theoretical model that clarifies several puzzling issues concerning the microscopic origin of flicker noise in graphene field-effect transistors (GraFET)

Kinetics and mechanism of arsenic removal using sulfide-modified nanoscale zerovalent iron

Sulphur modified nano zerovalent iron (S?nZVI) has shown considerable promise for removal of various aqueous contaminants. However studies utilizing S?nZVI for removal of aqueous inorganic arsenic (As) is relatively rare, which was studied in this work. Characterization of the synthesized S?nZVI showed typical core-shelled structure with distorted outer shell consisting of iron oxide and FeS. The removal rate of both As(III) and As(V) by S?nZVI was considerably enhanced compared to nZVI and highest As removal was observed at S/Fe ratio of 0.1 under acidic condition. Results showed slight decrease in As removal efficiencies for S?nZVI aged upto 48 h, with obvious drop in As removal efficiencies for longer aging time which although still exhibited higher reactivity than bare nZVI. Spectroscopic investigation showed sulphur amendment of nZVI completely altered the As sequestration mechanism compared to nZVI. While reduction of the adsorbed As(III) and As(V) was observed for bare nZVI, in contrast, uptake of As(III) and As(V) by S?nZVI involves adsorption as As(III) and As(V) oxyanion respectively with additional precipitation of As2S3. Overall, the study shows that incorporation of FeS on the surface of nZVI can be an effective modification strategy for efficient sequestration of As from contaminated water

Evaluation of Dengue NS1 Antigen Rapid Tests and ELISA Kits Using Clinical Samples

<div><p>Background</p><p>Early diagnosis of dengue virus (DENV) infection can improve clinical outcomes by ensuring close follow-up, initiating appropriate supportive therapies and raising awareness to the potential of hemorrhage or shock. Non-structural glycoprotein-1 (NS1) has proven to be a useful biomarker for early diagnosis of dengue. A number of rapid diagnostic tests (RDTs) and enzyme-linked immunosorbent assays (ELISAs) targeting NS1 antigen (Ag) are now commercially available. Here we evaluated these tests using a well-characterized panel of clinical samples to determine their effectiveness for early diagnosis.</p><p>Methodology/Principal Findings</p><p>Retrospective samples from South America were used to evaluate the following tests: (i) “Dengue NS1 Ag STRIP” and (ii) “Platelia Dengue NS1 Ag ELISA” (Bio-Rad, France), (iii) “Dengue NS1 Detect Rapid Test (1^st Generation)” and (iv) “DENV Detect NS1 ELISA” (InBios International, United States), (v) “Panbio Dengue Early Rapid (1^st generation)” (vi) “Panbio Dengue Early ELISA (2^nd generation)” and (vii) “SD Bioline Dengue NS1 Ag Rapid Test” (Alere, United States). Overall, the sensitivity of the RDTs ranged from 71.9%–79.1% while the sensitivity of the ELISAs varied between 85.6–95.9%, using virus isolation as the reference method. Most tests had lower sensitivity for DENV-4 relative to the other three serotypes, were less sensitive in detecting secondary infections, and appeared to be most sensitive on Day 3–4 post symptom onset. The specificity of all evaluated tests ranged from 95%–100%.</p><p>Conclusions</p><p>ELISAs had greater overall sensitivity than RDTs. In conjunction with other parameters, the performance data can help determine which dengue diagnostics should be used during the first few days of illness, when the patients are most likely to present to a clinic seeking care.</p></div

Device performance stratified by day post symptom onset and infection status.

<p>The diagnostic tests are shown on the X-axis, while the sensitivity of the device is shown in the Y-axis. Color of the bar denotes day PSO (A) or primary/secondary infection status (B).</p