Patterns of repeated diagnostic testing for COVID-19 in relation to patient characteristics and outcomes.

BACKGROUND: Whilst the COVID-19 diagnostic test has a high false-negative rate, not everyone initially negative is re-tested. Michigan Medicine, a primary regional centre, provided an ideal setting for studying testing patterns during the first wave of the pandemic. OBJECTIVES: To identify the characteristics of patients who underwent repeated testing for COVID-19 and determine if repeated testing was associated with downstream outcomes amongst positive cases. METHODS: Characteristics, test results, and health outcomes for patients presenting for a COVID-19 diagnostic test were collected. We examined whether patient characteristics differed with repeated testing and estimated a false-negative rate for the test. We then studied repeated testing patterns in patients with severe COVID-19-related outcomes. RESULTS: Patient age, sex, body mass index, neighbourhood poverty levels, pre-existing type 2 diabetes, circulatory, kidney, and liver diseases, and cough, fever/chills, and pain symptoms 14 days prior to a first test were associated with repeated testing. Amongst patients with a positive result, age (OR: 1.17; 95% CI: (1.05, 1.34)) and pre-existing kidney diseases (OR: 2.26; 95% CI: (1.41, 3.68)) remained significant. Hospitalization (OR: 7.88; 95% CI: (5.15, 12.26)) and ICU-level care (OR: 6.93; 95% CI: (4.44, 10.92)) were associated with repeated testing. The estimated false-negative rate was 23.8% (95% CI: (19.5%, 28.5%)). CONCLUSIONS: Whilst most patients were tested once and received a negative result, a meaningful subset underwent multiple rounds of testing. These results shed light on testing patterns and have important implications for understanding the variation of repeated testing results within and between patients.

Reaction Mechanism and Selectivity Control of Si Compound ALE Based on Plasma Modification and F-Radical Exposure.

In this work, atomic layer etching (ALE) of Si compounds using H2 or N2 plasma modification followed by fluorine radical exposure is discussed. It is shown that the H2 plasma modification process promotes the selective etching of SiN, SiC, and SiCO versus SiO2. The N2 plasma modification, on the other hand, enables the selective etching of SiC and SiCO versus SiN and SiO2. The origin of the etching selectivity between different Si compounds is investigated using a combination of in situ SE and FTIR supported by several ex situ analysis techniques. It is shown that the formation of a hydrogen-rich layer after plasma modification is essential to enable the ALE process. The hydrogen-rich layer can be formed due to ion and radicals of the modification plasma (H2 plasma modification) or be a result of the reconfiguration of hydrogen that is already present in the film (N2 plasma modification). The obtained insights are expected to further enhance the etching selectivity of Si compound ALE processes. Furthermore, it is anticipated that the process can be extended to many other compound materials such as Ti and Hf, as well as enable selective etching between their oxides, carbides, and nitrides.

Endogenous sex steroid hormones and glucose in a South-Asian population without diabetes: the Metabolic Syndrome and Atherosclerosis in South-Asians Living in America pilot study.

AIMS: To examine the associations between endogenous sex steroid hormones (oestradiol, testosterone and sex hormone-binding globulin) with diabetes risk in a South-Asian population living in the USA. METHODS: We used data from the Metabolic Syndrome and Atherosclerosis in South-Asians Living in America pilot study. The analytical sample included 60 women and 45 men of Asian Indian origin living in the San Francisco Bay Area, who were free from diabetes and cardiovascular disease and did not use exogenous sex steroids. Sex steroid hormone levels were assessed by validated conventional radioimmunoassays, and visceral and hepatic adiposity were assessed by computed tomography. We used multivariable regression to examine the association between endogenous sex steroid hormone levels (log-transformed) and fasting glucose and 2-h glucose levels in a series of sex-stratified models adjusted for age, waist circumference, visceral and hepatic adiposity, and insulin resistance. RESULTS: In age-adjusted models, lower levels of sex hormone-binding globulin (ß = -0.18, 95% CI -0.30, -0.06) and higher levels of free testosterone (ß = 0.14, 95% CI 0.02, 0.26) were associated with elevated fasting glucose levels in South-Asian women, whereas lower levels of sex hormone-binding globulin (ß = -0.14, 95% CI -0.26, -0.02) and lower levels of total testosterone (ß = -0.12, 95% CI -0.24, 0.00) were associated with elevated fasting glucose levels in South-Asian men. Adjustment for waist circumference, visceral adiposity and insulin resistance attenuated most of these associations, while adjustment for hepatic adiposity strengthened some of the observed associations. Similar results were found for 2-h glucose levels. CONCLUSIONS: Results were consistent with previous research, which suggests that endogenous sex steroid hormones are a risk factor for diabetes across multiple race/ethnic groups. Additional studies are needed to determine whether visceral fat is a mediator or confounder of associations between sex steroid hormone and glucose levels.

Modelling system dynamics and phytoplankton diversity at Ranchi lake using the carbon and nutrient mass balance equations.

Modelling system dynamics in a hyper-eutrophic lake is quite complex especially with a constant influx of detergents and sewage material which continually changes the state variables and interferes with the assessment of the chemical rhythm occurring in polluted conditions as compared to unpolluted systems. In this paper, a carbon and nutrient mass balance model for predicting system dynamics in a complex environment was studied. Studies were conducted at Ranchi lake to understand the altered environmental dynamics in hyper-eutrophic conditions, and its impact on the plankton community. The lake was monitored regularly for five years (2007 - 2011) and the data collected on the carbon flux, nitrates, phosphates and silicates was used to design a mass balance model for evaluating and predicting the system. The model was then used to correlate the chemical rhythm with that of the phytoplankton dynamics and diversity. Nitrates and phosphates were not limiting (mean nitrate and phosphate concentrations were 1.74 and 0.83 mgl⁻¹ respectively). Free carbon dioxide was found to control the system and, interacting with other parameters determined the diversity and dynamics of the plankton community. N/P ratio determined which group of phytoplankton dominated the community, above 5 it favoured the growth of chlorophyceae while below 5 cyanobacteria dominates. TOC/TIC ratio determined the abundance. The overall system was controlled by the availability of free carbon dioxide which served as a limiting factor.

Nasal cytokine responses to natural colds in asthmatic children.

BACKGROUND: The mechanisms by which viruses induce asthma exacerbations are not well understood. OBJECTIVE: We characterized fluctuations in nasal aspirate cytokines during naturally occurring respiratory viral infections in children with asthma. METHODS: Sixteen children underwent home collections of nasal aspirates when they were without cold symptoms and again during self-reported respiratory illnesses. The presence of viral infection was ascertained by multiplex PCR. Cytokines were measured using multiplex immune assay. mRNA expression for selected markers of viral infection was measured using RT-PCR. A cumulative respiratory symptom score was calculated for each day of measurement. Generalized estimated equations were used to evaluate associations between viral infection and marker elevation, and between marker elevation and symptom score. RESULTS: The 16 patients completed a total of 37 weeks of assessment (15 'well' weeks; 22 self-assessed 'sick' weeks). Viral infections were detected in 3 of the 'well' weeks and 17 of the 'sick' weeks (10 rhinovirus, three coronavirus, two influenza A, two influenza B, two respiratory syncytial virus, one parainfluenza). Compared to virus-negative well weeks, nasal aspirate IFN-γ, CXCL8/IL-8, CXCL10/IP-10, CCL5/RANTES, CCL11/eotaxin-1, CCL2/MCP-1, CCL4/MIP-1ß, CCL7/MCP-3, and CCL20/MIP3α protein levels increased during virus-positive sick weeks. Only a subset of cytokines (IFN-γ, CXCL8, CCL2, CCL4, CCL5, and CCL20) correlated with self-reported respiratory tract symptoms. While many aspirates were dilute and showed no mRNA signal, viral infection significantly increased the number of samples that were positive for IFN-λ1, IFN-λ2/3, TLR3, RIG-I, and IRF7 mRNA. CONCLUSIONS AND CLINICAL RELEVANCE: We conclude that in children with asthma, naturally occurring viral infections apparently induce a robust innate immune response including expression of specific chemokines, IFNs, and IFN-responsive genes.

Logistic regression analysis of biomarker data subject to pooling and dichotomization.

There is growing interest in pooling specimens across subjects in epidemiologic studies, especially those involving biomarkers. This paper is concerned with regression analysis of epidemiologic data where a binary exposure is subject to pooling and the pooled measurement is dichotomized to indicate either that no subjects in the pool are exposed or that some are exposed, without revealing further information about the exposed subjects in the latter case. The pooling process may be stratified on the disease status (a binary outcome) and possibly other variables but is otherwise assumed random. We propose methods for estimating parameters in a prospective logistic regression model and illustrate these with data from a population-based case-control study of colorectal cancer. Simulation results show that the proposed methods perform reasonably well in realistic settings and that pooling can lead to sizable gains in cost efficiency. We make recommendations with regard to the choice of design for pooled epidemiologic studies.

On the equivalence of posterior inference based on retrospective and prospective likelihoods: application to a case-control study of colorectal cancer.

The paper develops a class of priors that leads to equivalent posterior inference for odds ratio parameters based on prospective and retrospective models for categorical response data. The results are applicable to both unmatched and matched case-control studies. The results hold for a general class of link functions for categorical response. The proposed method can accommodate multiple and possibly ordered disease states. The results are applied to the analysis of discrete subtypes in an ongoing case-control study of colorectal cancer. A simulation study illustrates the need for carefully considering prior choices in Bayesian analysis of data collected under retrospective design.

Particulate matter concentrations in residences: an intervention study evaluating stand-alone filters and air conditioners.

UNLABELLED: This study, a randomized controlled trial, evaluated the effectiveness of free-standing air filters and window air conditioners (ACs) in 126 low-income households of children with asthma. Households were randomized into a control group, a group receiving a free-standing HEPA filter placed in the child's sleeping area, and a group receiving the filter and a window-mounted AC. Indoor air quality (IAQ) was monitored for week-long periods over three to four seasons. High concentrations of particulate matter (PM) and carbon dioxide were frequently seen. When IAQ was monitored, filters reduced PM levels in the child's bedroom by an average of 50%. Filter use varied greatly among households and declined over time, for example, during weeks when pollutants were monitored, filter use was initially high, averaging 84±27%, but dropped to 63±33% in subsequent seasons. In months when households were not visited, use averaged only 34±30%. Filter effectiveness did not vary in homes with central or room ACs. The study shows that measurements over multiple seasons are needed to characterize air quality and filter performance. The effectiveness of interventions using free-standing air filters depends on occupant behavior, and strategies to ensure filter use should be an integral part of interventions. PRACTICAL IMPLICATIONS: Environmental tobacco smoke (ETS) increased particulate matter (PM) levels by about 14 µg/m3 and was often detected using ETS-specific tracers despite restrictions on smoking in the house as reported on questionnaires administered to caregivers. PM concentrations depended on season, filter usage, relative humidity, air exchange ratios, number of children, outdoor PM levels, sweeping/dusting, and presence of a central air conditioner (AC). Free-standing air filters can be an effective intervention that provides substantial reductions in PM concentrations if the filters are used. However, filter use was variable across the study population and declined over the study duration, and thus strategies are needed to encourage and maintain use of filters. The variability in filter use suggests that exposure misclassification is a potential problem in intervention studies using filters. The installation of a room AC in the bedroom, intended to limit air exchange ratios, along with an air filter, did not lower PM levels more than the filter alone.

Hypertension with elevated levels of oxidized low-density lipoprotein and anticardiolipin antibody in the circulation of premenopausal Indian women chronically exposed to biomass smoke during cooking.

UNLABELLED: This study aims to investigate whether indoor air pollution (IAP) from biomass fuel use was associated with hypertension, platelet hyperactivity, and elevated levels of oxidized low-density lipoprotein (oxLDL) and anticardiolipin antibody (aCL). We enrolled 244 biomass fuel-using (median age 34 year) and 236 age-matched control women who cooked with liquefied petroleum gas (LPG). Enzyme-linked immunosorbent assay was used to measure oxLDL in plasma and aCL in serum, flow cytometry for P-selectin expression on platelet and reactive oxygen species (ROS) generation by leukocytes, aggregometry for platelet aggregation, spectrophotometry for superoxide dismutase (SOD) in erythrocytes, and laser photometer for particulate matter <10 and 2.5 µm in diameter (PM(10) and PM(2.5), respectively) in cooking areas. Biomass users had three times more particulate pollution in kitchen, had higher prevalence of hypertension (29.5 vs. 11.0% in control, P < 0.05), elevated oxLDL (170.6 vs. 45.9 U/l; P < 0.001), platelet P-selectin expression (9.1% vs. 2.4%), platelet aggregation (23.2 vs. 15.9 Ohm), raised aCL IgG (28.7% vs. 2.1%), IgM (8.6% of vs. 0.4%), and ROS (44%) but depleted (13%) SOD. After controlling potential confounders, the changes were positively associated with PM(10) and PM(2.5) in indoor air, suggesting a positive association between IAP and increased cardiovascular risk. PRACTICAL IMPLICATIONS: The study showing high risk of developing cardiovascular diseases (CVD) among poor, underprivileged women in their reproductive ages in rural India is important from public health perspectives. It may motivate the government and the regulatory agencies of the country to take a serious note of the indoor air pollution (IAP) from biomass fuel use as it threatens the health of millions of women, children, and the elderly who mostly stay indoor. We hope the findings will strengthen the demand for setting up a standard for indoor air quality in the country in the line of national ambient air quality standard. The findings may also inspire the authorities to take measures for the reduction in IAP by improving housing, kitchen ventilation, and cook stoves. Moreover, the parameters used in this study can be utilized for large, population-based studies to identify women at a higher risk of developing CVD so that medical intervention can be taken at the formative stage of a disease.

Growth inhibition of estrogen receptor positive human breast cancer cells by Taheebo from the inner bark of Tabebuia avellandae tree.

Selective estrogen receptor (ER) modulators are used as a therapy for ER+ clinical breast cancer, but they exhibit adverse effects. Herbal medicines may provide an alternative or complementary approach. Taheebo, extracted from the inner bark of the Tabebuia avellandae tree found in the Brazilian Amazon, exhibits selective anti-proliferative effects in carcinoma cell lines. The present study identifies the mechanistic leads for the inhibitory effects of Taheebo. Human breast carcinoma derived ER+MCF-7 cells were used as the model. Aqueous extract of Taheebo was the test compound. Cell cycle analysis, clonogenic assay, and global gene expression profiles were the quantitative parameters. Taheebo treatment resulted in a dose/time-dependent growth inhibition (S phase arrest, reduced clonogeneticity) and initiation of apoptosis (chromatin condensation). A 6-h treatment with 1.5 mg/ml Taheebo modulated the gene expression of G2 specific cyclin B1 (-2.0-fold); S phase specific PCNA (-2.0-fold) and OKL38 (+11.0-fold); apoptosis specific GADD-45 family (+1.9-5.4-fold), Caspases (+1.6-1.7-fold), BCL-2 family (-1.5-2.5-fold), estrogen responsive ESR1 (-1.5-fold), and xeno-biotic metabolism specific CYP 1A1 (+19.8 fold) and CYP 1B1 (+7.9-fold). The anti-proliferative effects of Taheebo correlate with down-regulated cell cycle regulatory and estrogen responsive genes, and up-regulated apoptosis specific and xeno-biotic metabolism specific genes. These data validate a rapid mechanistic approach to prioritize efficacious herbal medicines, thereby complementing the existing endocrine therapy for breast cancer.

Nutrient cycling in a simulated pond ecosystem.

Mathematical modeling of ecosystems requires a considerable amount of knowledge about the subsystems functioning within the broad framework and the various rate processes and transfer coefficients that control the dynamic aspects. A detailed analysis of the transfer rates and budget of inorganic carbon and nutrients in a simulated pond was conducted for assessment and comparison with aquatic bodies that undergo cultural eutrophication. In these systems the processes are complicated by a variety of inputs. Such inputs interfere with the assessment of lake background conditions and water quality. We used the compartmental model of biogeochemical cycling to calculate transfer rate of inorganic carbon and nutrients through various processes. The major external variables or forcing functions considered were light and temperature, while the state variables included the biotic and the abiotic compartments. The major processes studied were: photosynthesis, respiration and decomposition that play an important partin balancing the nutrient content of the system and maintain a dynamic equilibrium. The study illustrates how computational modeling studies are useful for analysis and management of systems for control and optimization of processes. The system shows a perfect cycling of carbon and the rate of withdrawal is equal to the return keeping the system in balance. About 0.284 m moles l(-1) is withdrawn from the reservoir for primary production each day and returned back through respiration and decomposition. The concentration of nitrates and phosphates resonate in tune with the utilization of carbon and productivity.

Evaluation of socio-economic factors causing discontinuation of epilepsy treatment resulting in seizure recurrence: a study in an urban epilepsy clinic in India.

BACKGROUND AND PURPOSE: The prevalence rate of epilepsy in India ranges between 4.15 and 7.03 per 1000 population. In the developing countries, the major problems of epilepsy are lying in the treatment gap and discontinuation of treatment due to various adverse socio-economic factors. The objective of this study was to evaluate the rate of discontinuation of epilepsy treatment and its related socio-economic factors responsible for discontinuation. MATERIAL AND METHODS: Among 1450 patients with epilepsy who were recurrently followed up at an intervals of 2 months from 05 January to 06 January; 620 patients discontinued their treatment. Among them 88.7% patient had breakthrough seizures for more than in two occasions. Socio-economic factors in respect to the treatment were evaluated during the follow-up period vis-a-vis income and expenditure, unemployment status, negative attitude towards medical treatment, non-availability of drugs locally, co-morbid psychiatric and other illnesses, polytherapy and socialillusional thoughts about epilepsy. RESULTS: Discontinuation of epilepsy treatment was detected in 42.75% (n = 620) of total patients resulting in recurrence of seizures. Reasons for discontinuation were multiple in most of the cases. The discontinued group had an average annual cost of treatment and income of Rs. 5500 ($110) and Rs. 12,800 ($256), respectively, amounting to 40% of their total income being expended for the cost of the treatment, while in continued group annual cost of treatment and income were Rs. 4500 ($ = 90) and Rs. 24,400 ($ = 580) respectively amounting to only 18% of the total income (p < 0.001) for the cost of treatment. Among the discontinued group, 90% of the patients reported the cost factors, 29.09% due to the unemployment, 20% from the frustration and despair, 20.09% due to non-availability of medicines locally, 17.27% spiritual illusional thoughts about epilepsy, 10% for marital disharmony were the causes for discontinuation of treatment. In the discontinued group, 10% got polytherapy against 9.03% in the continued group (p > 0.01), co-morbid psychiatric illnesses were observed in 4.54% against 3.25% in the continued group (p > 0.10). CONCLUSION: The study showed a significant number of patients (42.75%) discontinued epilepsy treatment within 1 year due to poor knowledge regarding the problem of discontinuation, cost and income disparity, unemployment, spiritual illusional thoughts about epilepsy, frustration and mental impairment, lack of uniform availability of drugs in local market. To tide these shortcomings, uniform availability of cheaper antiepileptic drugs with adequate information and communication regarding the disease and upliftment of socio-economic status are to be ensured.

Application of low-cost Gallium Arsenide light-emitting-diodes as kerma dosemeter and fluence monitor for high-energy neutrons.

Displacement damage (DD) caused by fast neutrons in unbiased Gallium Arsenide (GaAs) light emitting diodes (LED) resulted in a reduction of the light output. On the other hand, a similar type of LED irradiated with gamma rays from a (60)Co source up to a dose level in excess of 1.0 kGy (1.0 x 10(5) rad) was found to show no significant drop of the light emission. This phenomenon was used to develop a low cost passive fluence monitor and kinetic energy released per unit mass dosemeter for accelerator-produced neutrons. These LED-dosemeters were used to assess the integrated fluence of photoneutrons, which were contaminated with a strong bremsstrahlung gamma-background generated by the 730 MeV superconducting electron linac driving the free electron laser in Hamburg (FLASH) at Deutsches Elektronen-Synchrotron. The applications of GaAs LED as a routine neutron fluence monitor and DD precursor for the electronic components located in high-energy accelerator environment are highlighted.

Serological aspects of Dengue fever and its correlation with clinical features in a recent febrile outbreak.

The study was done to assess correlation between serology and clinical features of Dengue fever at Burdwan Medical College, where after clinical examination, blood samples were processed by E.I.A. Of 139 cases, mostly between 1 to 20 years, Male-Female ratio was 80:59. Bleeding manifestation was observed only in 3 cases, and Lymphadenopathy, Myocarditis were uncommon features. Few patients have biphasic temperature. Fever and severity of symptoms did not have correlation. Patients' blood was examined for Dengue viruses, with only 44.6% positivity. Correlation exists between illness duration and antibody titer. [r = 0.41; (P < 0.01)]. Fever other, than Dengue also exhibited similar symptoms, but optical density in EIA test was less. As high fever with similar symptoms may be due to causes other than Dengue, thorough search for other viral infection namely Chikungunya should be done in endemic areas also.

Exciton Emission Intensity Modulation of Monolayer MoS2 via Au Plasmon Coupling.

Modulation of photoluminescence of atomically thin transition metal dichalcogenide two-dimensional materials is critical for their integration in optoelectronic and photonic device applications. By coupling with different plasmonic array geometries, we have shown that the photoluminescence intensity can be enhanced and quenched in comparison with pristine monolayer MoS2. The enhanced exciton emission intensity can be further tuned by varying the angle of polarized incident excitation. Through controlled variation of the structural parameters of the plasmonic array in our experiment, we demonstrate modulation of the photoluminescence intensity from nearly fourfold quenching to approximately threefold enhancement. Our data indicates that the plasmonic resonance couples to optical fields at both, excitation and emission bands, and increases the spontaneous emission rate in a double spacing plasmonic array structure as compared with an equal spacing array structure. Furthermore our experimental results are supported by numerical as well as full electromagnetic wave simulations. This study can facilitate the incorporation of plasmon-enhanced transition metal dichalcogenide structures in photodetector, sensor and light emitter applications.

HPLC detection of plasma concentrations of diclofenac in human volunteers administered with povidone-ethylcellulose-based experimental transdermal matrix-type patches.

By developing a high-performance liquid chromatography (HPLC) method, we estimated the blood concentrations of diclofenac in human volunteers administered with the transdermal patches prepared with povidone-ethylcellulose and oral diclofenac tablets. Drug-excipient interaction studies were done using the FTIR technique. The external morphology of the prepared patch before and after application to human skin was analyzed with scanning electron microscopy. FTIR studies revealed that there was no predominant interaction between the drug and polymers. In vivo studies revealed that the average concentrations of drug in plasma were 376, 1562, 2953, 2902, 2864, and 2948 ng/ml after 2, 4, 8, 24, 30, and 48 h from patches each containing 50 mg of diclofenac diethylamine, respectively, and the mean concentrations of drug in plasma after the oral administration of marketed tablet containing 50 mg diclofenac sodium were 383.7, 2569, 3693.5, 162.5, and 55.3 ng/ml at 2, 4, 8, 24, and 30 h after oral administration. Values of Cmax were 3693.5 after oral administration and 2953.8 ng/ml in the case of transdermal application. From this study, we have achieved the sustained blood level of diclofenac from the experimental patches along with an analytical method based on HPLC to determine the diclofenac blood level.

Effects of 12-O-tetradecanoylphorbol-13-acetate on fibroblasts from individuals genetically predisposed to cancer.

The purpose of the present study was to determine whether skin fibroblasts from individuals, either with an inherited predisposition to cancer or with genetic disorders usually associated with a high risk of cancer, can be oncogenically transformed in vitro by a tumor promoter alone. The effects of chronic and limited applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) on several properties that are associated with transformation were examined using skin fibroblasts from individuals with polyposis coli, a familial cancer syndrome, xeroderma pigmentosum, Fanconi's anemia, and trisomy 21. The results of this study show that TPA treatment induces similar changes on cellular morphology, growth rate, saturation density, epidermal growth factor binding, and cytoskeleton in fibroblasts from both normal and genetically predisposed individuals. None of these cell lines, however, acquired anchorage-independent growth or unlimited growth potential in culture after chronic application of TPA. These observations suggest clearly that skin fibroblasts from individuals with either a genetic predisposition to or a high risk of cancer may not exist in a preneoplastic or "initiated" state susceptible to oncogenic transformation by TPA alone and that the mechanism of genetically determined cancer induction may be different from that of chemical carcinogenesis.

Altered biochemical properties of actin in normal skin fibroblasts from individuals predisposed to dominantly inherited cancers.

The data presented here show that normal skin fibroblasts from individuals with dominantly inherited retinoblastoma, polyposis coli, and nevoid basal cell carcinoma (predisposed cells), grown in the presence of [35S]methionine, contain more than 2.5-fold [35S]methionine-labeled actin as compared to normal fibroblasts from individuals without a prior history of predisposition to cancer (normal cells). The rate of incorporation of [35S]methionine into actin in predisposed cells is rapid and is not correlated with an increase in the total protein and actin contents of the cells, in the intracellular pool size of [35S]methionine, or in the synthesis of beta-actin-specific mRNA, as compared to normal cells. However, the half-life of actin in predisposed cells is less than 5 h, as compared to at least 48 h for normal cells. The significantly reduced half-life of actin and an increased incorporation of [35S]methionine specifically into actin in all predisposed cells studied may represent an inherited biochemical defect which leads to cytoskeletal disorganization previously observed in these cells. It can be speculated that the altered properties of actin in predisposed cells may be caused by the same genetic lesion(s) which is responsible for the induction of dominantly inherited cancers.

Cation exchange synthesis of uniform PbSe/PbS core/shell tetra-pods and their use as near-infrared photodetectors.

In this work we explore the preparation of complex-shaped semiconductor nanostructures composed of different materials via a cationic exchange process in which the cations of the original semiconductor nanostructure are replaced by cations of different metals with preservation of the shape and the anionic framework of the nanocrystals. Utilizing this cation exchange method, we synthesized two new tetrapods for the first time: Cu2-xSe/Cu2-xS and PbSe/PbS, both prepared from CdSe/CdS tetrapods as 'templates'. We also fabricated near-infrared (NIR) photodetectors with a very simple architecture comprising a PbSe/PbS tetrapod layer between two Au electrodes on a glass substrate. When illuminated by a NIR laser, these devices are capable of achieving a responsivity of 11.9 A W(-1) without the use of ligand-exchange processes, thermal annealing or hybrid device architecture. Transient absorption spectroscopy was carried out on these PbSe/PbS tetrapods, the results of which suggest that the branched morphology contributes in part to device performance. Investigation of the charge dynamics of the PbSe/PbS tetrapods revealed an extremely long-lived exciton recombination lifetime of ∼17 ms, which can result in enhanced photoconductive gain. Overall, these heterostructured tetrapods showcase simultaneously the importance of nanoparticle shape, band structure, and surface chemistry in the attainment of NIR photodetection.