Demographic history and the efficacy of selection in the globally invasive mosquito Aedes aegypti.

Aedes aegypti is the main vector species of yellow fever, dengue, zika and chikungunya. The species is originally from Africa but has experienced a spectacular expansion in its geographic range to a large swath of the world, the demographic effects of which have remained largely understudied. In this report, we examine whole-genome sequences from 6 countries in Africa, North America, and South America to investigate the demographic history of the spread of Ae. aegypti into the Americas its impact on genomic diversity. In the Americas, we observe patterns of strong population structure consistent with relatively low (but probably non-zero) levels of gene flow but occasional long-range dispersal and/or recolonization events. We also find evidence that the colonization of the Americas has resulted in introduction bottlenecks. However, while each sampling location shows evidence of a past population contraction and subsequent recovery, our results suggest that the bottlenecks in America have led to a reduction in genetic diversity of only ~35% relative to African populations, and the American samples have retained high levels of genetic diversity (expected heterozygosity of ~0.02 at synonymous sites) and have experienced only a minor reduction in the efficacy of selection. These results evoke the image of an invasive species that has expanded its range with remarkable genetic resilience in the face of strong eradication pressure.

Cost and Utilization Implications of a Health Plan's Home-Based Palliative Care Program.

Background: A California-based health plan offered home-based palliative care (HBPC) to members who needed support at home but did not yet qualify for hospice. Objectives: This study compares hospital and emergency department (ED) utilization and costs and mortality for individuals receiving HBPC to a cohort not receiving palliative care services (Usual Care). Design: This is an observational retrospective study using claims data covering a prestudy period and a study period during which time half of the study population received HBPC services. Setting/Subjects: Seriously ill individuals who received HBPC were matched with those receiving Usual Care using a propensity-based matching algorithm. Intervention: Interdisciplinary teams from home health and hospice agencies provided HBPC services. Measurements: Outcome measures included hospital and ED utilization and cost before and during the study period and mortality during the study period. Results: For both groups, hospital and ED utilization and associated costs were higher during the prestudy period than during the study period. No differences were found in outcome measures between groups during the study period. Average time in the study period was longer for the HBPC group than that in the Usual Care group, indicating that they lived longer or transitioned to hospice later. Conclusion: Although individuals in both groups were living with serious illnesses for which worsening health and increased acute care utilization are expected over time, both groups had reduced acute care utilization and costs during the study period compared with the prestudy period. Reduced utilization and costs were equivalent for both groups.

Comparison of injuries among motorcycle, moped and bicycle traffic accident victims.

OBJECTIVE: Motorcycles, moped scooters and bicycles are commonly involved in traffic accidents and riders often suffer significant morbidity and mortality. The aim of this study is to compare and categorize the different injury patterns and fractures suffered by riders of each vehicle type after a traffic accident. METHODS: Data from a level 1 trauma center in Las Vegas, Nevada were analyzed. Traffic accident victims riding a motorcycle, moped, or bicycle from 2013 to 2017 were included. Injury location and fracture location were assigned to six and sixteen categorical locations, respectively. Descriptive statistics, including frequency counts for categorical data and mean for continuous data, were calculated for the full sample and for each of the vehicle types. Logistic regression was performed on race, categorized age, vehicle type and helmet use to calculate adjusted odds ratios for injury type between the three groups. RESULTS: Of the 2115 patients, 1372 were motorcyclists, 356 were moped scooter riders and 387 were bicyclists. Overall the vast majority of injuries reported were of the extremities or pelvic girdle (62.2%), and this was true regardless of vehicle type. Head and neck injuries were significantly more common in bicyclists (39.5%) and moped riders (34.6%), than in motorcyclists (22.7%). Helmet use was substantially lower in the moped (34%) and bicycle (20%) groups compared to the motorcycle group (85%). The most common fractures regardless of vehicle type were of the skull/face, rib, vertebral, and tibia/fibula with slight variations between vehicle groups. CONCLUSION: Similarities were seen in the most common fracture and injury patterns between the three groups. Head and neck injuries were much more common in moped and bicycle riders compared to motorcyclists. This is most likely due to the significantly higher percentage of motorcycle riders who wore a helmet. Counseling regarding helmet and protective equipment use, especially among moped and bicycle riders is essential to reduce head injuries.

Association of Generic Competition With Price Decreases in Physician-Administered Drugs and Estimated Price Decreases for Biosimilar Competition.

Importance: Price decreases of biologic and biosimilar products in Medicare Part B have been minimal, even with biosimilar competition. Medicare reimburses clinicians for biologics and biosimilars differently than for brand-name and generic drugs, which has generated greater price reductions. Objective: To characterize the nature of price competition among brand-name and generic drugs under Medicare Part B and to estimate the cost savings to the program of subjecting biologic and biosimilar therapies to a similar price competition. Design, Setting, and Participants: This cohort study analyzed all brand-name drugs and their approved generic versions as well as biologics and biosimilars that were reimbursed under Medicare Part B from quarter 1 of 2005 to quarter 2 of 2021. Two separate data sets were created: brand-name and generic drugs as well as biologics and biosimilars data sets. Brand-name products with generic versions that were introduced before 2005 were excluded, and so were vaccines. Exposures: Number of generic and biosimilar competitors over time. Main Outcomes and Measures: Price change as a percentage of the brand-name drug or biologic price in the quarter before generic or biosimilar competition. Price change was modeled using a linear, fixed-effects time series regression, with the number of generic or biosimilar competitors as the main covariate. Time was expressed as the number of quarters since the first generic or biosimilar competitor entered the market. Savings were estimated by projecting the regression model of brand-name and generic drug competition to observed biologic and biosimilar competition and by applying the estimated price reduction to actual Medicare spending for those products from 2015 to 2019. Results: Of the 988 Healthcare Common Procedure Coding System codes identified, 50 (5.0%) met the inclusion criteria for the brand-name and generic drug data set and 28 (2.8%) met the criteria for the biologic and biosimilar data set. The first generic competitor was associated with reduced drug prices by 17.0%, the second competitor with a 39.5% decrease, the third competitor with a 52.5% decrease, and the fourth and more competitors with a 70.2% decrease (price decline was measured from brand-name drug price before the first generic competitor rather than from price established with fewer competitors). If biologics and biosimilars were subject to the same Medicare reimbursement framework as brand-name and generic drugs, Medicare spending on these products was estimated to have been 26.6% lower ($1.6 billion) from 2015 to 2019. Conclusions and Relevance: This study found minimal uptake of biosimilars and limited price reductions for biologics and biosimilars under the current Medicare Part B reimbursement policy. Adopting the bundled biosimilar reimbursement structure for biologic and biosimilar therapies may be associated with substantial savings and encourage greater biosimilar market entry.

Association of dementia diagnosis with urinary tract infection in the emergency department.

OBJECTIVES: Overdiagnosis of urinary tract infections (UTI) among people living with dementia is a nationally recognized problem associated with morbidity from antibiotics as well as multidrug-resistant bacteria. However, whether this problem also exists in the emergency department (ED) is currently unknown. METHODS: To examine the association between dementia and UTI diagnosis in the ED we performed a retrospective analysis of Medicare beneficiaries older than 65 years old who presented to an ED in 2016. A diagnosis of UTI was present in 58,580 beneficiaries, and 321,479 beneficiaries without a diagnosis of UTI served as the comparison group. Our logistic regression model controlled for dementia, older age, female sex, Medicaid status, skilled nursing facility residence, history of prostate cancer, recent urinary catheter use, recurrent UTI, and multiple comorbidities. RESULTS: In our model, people living with dementia had over twice the odds (odds ratio = 2.27, 95% confidence interval = 2.21, 2.33) of being diagnosed with a UTI in the ED compared to those without dementia despite their lower prevalence of symptoms and signs localizing to the genitourinary tract (3.8% vs 8.9%, respectively). CONCLUSION: This is the first study from a national database that examines the association of dementia with UTI diagnosis among older adults who visit the ED. Our study could not establish whether the UTI diagnoses in the ED were accurate but does imply a disproportionate burden of UTI diagnoses in people living with dementia despite their lower prevalence of clinical criterion. Antimicrobial stewardship in the ED should address the complexity of UTI diagnosis in dementia.

30-Day Emergency Department Revisit Rates among Older Adults with Documented Dementia.

OBJECTIVES: Published literature on national emergency department (ED) revisit rates among older adults with dementia is sparse, despite anecdotal evidence of higher ED utilization. Thus we evaluated the odds ratio (OR) of 30-day ED revisits among older adults with dementia using a nationally representative sample. DESIGN: We assessed the frequency of claims associated with a 30-day ED revisit among Medicare beneficiaries with and without a dementia diagnosis before or at index ED visit. We used a logistic regression model controlling for dementia, age, sex, race, region, Medicaid status, transfer to a skilled nursing facility after ED, primary care physician use 12 months before index, and comorbidity. SETTING: A nationally representative sample of claims data for Medicare beneficiaries aged 65 and older who maintained continuous fee-for-service enrollment during 2015 and 2016. Only outpatient claims associated with an ED visit between January 2016 and November 2016 were included as a qualifying index encounter. PARTICIPANTS: We identified 240 249 patients without dementia and 54 622 patients for whom a dementia code was recorded in the year before the index encounter in 2016. RESULTS: Our results indicate a significant difference in unadjusted 30-day ED revisit rates among those with an ED dementia diagnoses (22.0%) compared with those without (13.9%). Our adjusted results indicated that dementia is a significant predictor of 30-day ED revisits (P < .0001). Those with a dementia diagnosis at or before the index ED visit were more likely to have experienced an ED revisit within 30 days (OR = 1.27; 95% confidence interval = 1.24-1.31). CONCLUSION: Dementia diagnoses were a significant predictor of 30-day ED revisits. Further research should assess potential reasons why dementia is associated with markedly higher revisit rates, as well as opportunities to manage and transition dementia patients from the ED back to the community more effectively. J Am Geriatr Soc 67:2254-2259, 2019.

A Method for Segmenting Medicare Expenditures to Inform Cost Effective Care Delivery for Older Adults.

INTRODUCTION: Faced with growing populations of older, medically complex patients, health systems are now incentivized to deliver cost-effective, high-value care. We evaluated a new method that builds upon existing Medicare spending concentration studies to further segment these expenditures, revealing use patterns to inform care redesign. METHODS: We obtained monthly Medicare expenditure data and derived baseline comparison data using typical methods for identifying a yearly high-cost subpopulation. We then applied the new methodology, ordering monthly patient expenditures from highest to lowest to more extensively segment the baseline data. Our evaluation examined the following within the new more extensive segmentation: monthly expenditure distribution, corresponding patient counts, and occupancy of specific patient subgroups within the extended segmentation of baseline data. RESULTS: Compared to the baseline data, we found further spending concentration, with 16.7 percent of high-cost patients being responsible for about two-thirds of baseline expenditures. The remaining 83.3 percent of the high-cost subpopulation exhibited lower spending, collectively accounting for about one third of baseline expenditures. Additionally, we found that unique patient subgroups occupied different segments over time, with specific subgroups comprising 8.3 percent of the study subpopulation patients migrating into and out of each highest spending segment, accounting for almost half of monthly baseline expenditures. CONCLUSIONS: With monthly health care expenditures concentrated among small numbers of migrating patients, our evaluation suggested potential cost-effectiveness in tiered care delivery models, where small subgroups receive direct, active care interactions, while the remainder experience surveillance-level care, designed to both address ongoing medical needs and to detect emergent migration.

Parental legacy, demography, and admixture influenced the evolution of the two subgenomes of the tetraploid Capsella bursa-pastoris (Brassicaceae).

Allopolyploidy is generally perceived as a major source of evolutionary novelties and as an instantaneous way to create isolation barriers. However, we do not have a clear understanding of how two subgenomes evolve and interact once they have fused in an allopolyploid species nor how isolated they are from their relatives. Here, we address these questions by analyzing genomic and transcriptomic data of allotetraploid Capsella bursa-pastoris in three differentiated populations, Asia, Europe, and the Middle East. We phased the two subgenomes, one descended from the outcrossing and highly diverse Capsella grandiflora (CbpCg) and the other one from the selfing and genetically depauperate Capsella orientalis (CbpCo). For each subgenome, we assessed its relationship with the diploid relatives, temporal changes of effective population size (Ne), signatures of positive and negative selection, and gene expression patterns. In all three regions, Ne of the two subgenomes decreased gradually over time and the CbpCo subgenome accumulated more deleterious changes than CbpCg. There were signs of widespread admixture between C. bursa-pastoris and its diploid relatives. The two subgenomes were impacted differentially depending on geographic region suggesting either strong interploidy gene flow or multiple origins of C. bursa-pastoris. Selective sweeps were more common on the CbpCg subgenome in Europe and the Middle East, and on the CbpCo subgenome in Asia. In contrast, differences in expression were limited with the CbpCg subgenome slightly more expressed than CbpCo in Europe and the Middle-East. In summary, after more than 100,000 generations of co-existence, the two subgenomes of C. bursa-pastoris still retained a strong signature of parental legacy but their evolutionary trajectory strongly varied across geographic regions.

Association Between Physical Therapy in the Emergency Department and Emergency Department Revisits for Older Adult Fallers: A Nationally Representative Analysis.

OBJECTIVES: To determine whether providing physical therapy (PT) services in the emergency department (ED) improves outcomes for older adults who fall. DESIGN: We used Medicare claims data to examine differences in recurrent fall-related ED revisit rates of older adults who presented to the ED for a ground-level fall and whether they received PT services in the ED. Our logistic regression model controlled for age, sex, Medicaid eligibility, acute injury, and certain known chronic comorbidities associated with risk of falling. SETTING: We analyzed national 2012-13 Medicare claims data for individuals aged 65 and older. PARTICIPANTS: This was a claims-based analysis. We defined an index visit as any ED claim that included an International Classification of Diseases, Ninth Revision, Clinical Modification E-Code indicating a ground-level fall. Visits resulting in admission were excluded, as were claims associated with an individual who died during follow-up; 17,975 of the 560,277 claims for eligible outpatient index visits included revenue center codes for PT services. MEASUREMENTS: We calculated the proportion of index visits associated with a fall-related ED revisit within 30 and 60 days and assessed differences in these proportions between individuals who did and did not receive PT services in the ED. RESULTS: Receiving PT services in the ED during an index visit for a ground-level fall was associated with a significantly lower likelihood of a fall-related ED revisit within 30 days (odds ratio (OR)=0.655, p<.001) and 60 days (OR=0.684, p<.001). CONCLUSION: Expanding PT services in the ED may reduce future fall-related ED use of older adults. Additional analyses could assess characteristics of individuals receiving PT in the ED and follow-up PT use after discharge. J Am Geriatr Soc 66:2205-2212, 2018.

Delirium as a predictor of mortality in US Medicare beneficiaries discharged from the emergency department: a national claims-level analysis up to 12 months.

BACKGROUND: Delirium is common among seniors discharged from the emergency department (ED) and associated with increased risk of mortality. Prior research has addressed mortality associated with seniors discharged from the ED with delirium, however has generally relied on data from one or a small number of institutions and at single time points. OBJECTIVES: Analyse mortality rates among seniors discharged from the ED with delirium up to 12 months at the national level. DESIGN: Retrospective cohort study. SETTING: Analysed data from the Centers for Medicare & Medicaid Services limited data sets for 2012-2013. PARTICIPANTS: Medicare fee-for-service beneficiaries aged 65 years or older discharged from the ED. We focused on new incident cases of delirium, patients with any prior claims for delirium, hospice claims or end-stage renal disease were excluded. Sample size included 26 245 delirium claims, and a randomly selected sample of 262 450 controls. OUTCOME MEASURES: Mortality within 12 months after discharge from the ED, excluding patients transferred or admitted as inpatients. RESULTS: Among all beneficiaries, 46 508 (16.1%) died within 12 months, of which 39 404 (15.0%) were in the non-delirium (ie, control group) and 7104 (27.1%) were in the delirium cohort, respectively. Mortality was strongest at 30 days with an adjusted HR of 4.82 (95% CI 4.60 to 5.04). Over time, delirium was consistently associated with increased mortality risk compared with controls up to 12 months (HR 2.07; 95% CI 2.01 to 2.13). Covariates that affected mortality included older age, comorbidity and presence of dementia. CONCLUSIONS: Our results demonstrate delirium is a significant marker of mortality among seniors in the ED, and mortality risk is most salient in the first 3 months following an ED visit. Given the significant clinical and financial implications, there is a need to increase delirium screening and management within the ED to help identify and treat this potentially fatal condition.

Coevolution between transposable elements and recombination.

One of the most striking patterns of genome structure is the tight, typically negative, association between transposable elements (TEs) and meiotic recombination rates. While this is a highly recurring feature of eukaryotic genomes, the mechanisms driving correlations between TEs and recombination remain poorly understood, and distinguishing cause versus effect is challenging. Here, we review the evidence for a relation between TEs and recombination, and discuss the underlying evolutionary forces. Evidence to date suggests that overall TE densities correlate negatively with recombination, but the strength of this correlation varies across element types, and the pattern can be reversed. Results suggest that heterogeneity in the strength of selection against ectopic recombination and gene disruption can drive TE accumulation in regions of low recombination, but there is also strong evidence that the regulation of TEs can influence local recombination rates. We hypothesize that TE insertion polymorphism may be important in driving within-species variation in recombination rates in surrounding genomic regions. Furthermore, the interaction between TEs and recombination may create positive feedback, whereby TE accumulation in non-recombining regions contributes to the spread of recombination suppression. Further investigation of the coevolution between recombination and TEs has important implications for our understanding of the evolution of recombination rates and genome structure.This article is part of the themed issue 'Evolutionary causes and consequences of recombination rate variation in sexual organisms'.

Low temperature thermal ALD of a SiNx interfacial diffusion barrier and interface passivation layer on SixGe1- x(001) and SixGe1- x(110).

Atomic layer deposition of a silicon rich SiNx layer on Si0.7Ge0.3(001), Si0.5Ge0.5(001), and Si0.5Ge0.5(110) surfaces has been achieved by sequential pulsing of Si2Cl6 and N2H4 precursors at a substrate temperature of 285 °C. XPS spectra show a higher binding energy shoulder peak on Si 2p indicative of SiOxNyClz bonding while Ge 2p and Ge 3d peaks show only a small amount of higher binding energy components consistent with only interfacial bonds, indicating the growth of SiOxNy on the SiGe surface with negligible subsurface reactions. Scanning tunneling spectroscopy measurements confirm that the SiNx interfacial layer forms an electrically passive surface on p-type Si0.70Ge0.30(001), Si0.50Ge0.50(110), and Si0.50Ge0.50(001) substrates as the surface Fermi level is unpinned and the electronic structure is free of states in the band gap. DFT calculations show that a Si rich a-SiO0.4N0,4 interlayer can produce lower interfacial defect density than stoichiometric a-SiO0.8N0.8, substoichiometric a-Si3N2, or stoichiometric a-Si3N4 interlayers by minimizing strain and bond breaking in the SiGe by the interlayer. Metal-oxide-semiconductor capacitors devices were fabricated on p-type Si0.7Ge0.3(001) and Si0.5Ge0.5(001) substrates with and without the insertion of an ALD SiOxNy interfacial layer, and the SiOxNy layer resulted in a decrease in interface state density near midgap with a comparable Cmax value.

Repeated Inactivation of the First Committed Enzyme Underlies the Loss of Benzaldehyde Emission after the Selfing Transition in Capsella.

The enormous species richness of flowering plants is at least partly due to floral diversification driven by interactions between plants and their animal pollinators [1, 2]. Specific pollinator attraction relies on visual and olfactory floral cues [3-5]; floral scent can not only attract pollinators but also attract or repel herbivorous insects [6-8]. However, despite its central role for plant-animal interactions, the genetic control of floral scent production and its evolutionary modification remain incompletely understood [9-13]. Benzenoids are an important class of floral scent compounds that are generated from phenylalanine via several enzymatic pathways [14-17]. Here we address the genetic basis of the loss of floral scent associated with the transition from outbreeding to selfing in the genus Capsella. While the outbreeding C. grandiflora emits benzaldehyde as a major constituent of its floral scent, this has been lost in the selfing C. rubella. We identify the Capsella CNL1 gene encoding cinnamate:CoA ligase as responsible for this variation. Population genetic analysis indicates that CNL1 has been inactivated twice independently in C. rubella via different novel mutations to its coding sequence. Together with a recent study in Petunia [18], this identifies cinnamate:CoA ligase as an evolutionary hotspot for mutations causing the loss of benzenoid scent compounds in association with a shift in the reproductive strategy of Capsella from pollination by insects to self-fertilization.

angsd-wrapper: utilities for analysing next-generation sequencing data.

High-throughput sequencing has changed many aspects of population genetics, molecular ecology and related fields, affecting both experimental design and data analysis. The software package angsd allows users to perform a number of population genetic analyses on high-throughput sequencing data. angsd uses probabilistic approaches which can directly make use of genotype likelihoods; thus, SNP calling is not required for comparative analyses. This takes advantage of all the sequencing data and produces more accurate results for samples with low sequencing depth. Here, we present angsd-wrapper, a set of wrapper scripts that provides a user-friendly interface for running angsd and visualizing results. angsd-wrapper supports multiple types of analyses including estimates of nucleotide sequence diversity neutrality tests, principal component analysis, estimation of admixture proportions for individual samples and calculation of statistics that quantify recent introgression. angsd-wrapper also provides interactive graphing of angsd results to enhance data exploration. We demonstrate the usefulness of angsd-wrapper by analysing resequencing data from populations of wild and domesticated Zea. angsd-wrapper is freely available from https://github.com/mojaveazure/angsd-wrapper.

The influence of surface preparation on low temperature HfO2 ALD on InGaAs (001) and (110) surfaces.

Current logic devices rely on 3D architectures, such as the tri-gate field effect transistor (finFET), which utilize the (001) and (110) crystal faces simultaneously thus requiring passivation methods for the (110) face in order to ensure a pristine 3D surface prior to further processing. Scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and correlated electrical measurement on MOSCAPs were utilized to compare the effects of a previously developed in situ pre-atomic layer deposition (ALD) surface clean on the InGaAs (001) and (110) surfaces. Ex situ wet cleans are very effective on the (001) surface but not the (110) surface. Capacitance voltage indicated the (001) surface with no buffered oxide etch had a higher C(max) hypothesized to be a result of poor nucleation of HfO2 on the native oxide. An in situ pre-ALD surface clean employing both atomic H and trimethylaluminum (TMA) pre-pulsing, developed by Chobpattana et al. and Carter et al. for the (001) surface, was demonstrated to be effective on the (110) surface for producing low D(it) high C(ox) MOSCAPs. Including TMA in the pre-ALD surface clean resulted in reduction of the magnitude of the interface state capacitance. The XPS studies show the role of atomic H pre-pulsing is to remove both carbon and oxygen while STM shows the role of TMA pre-pulsing is to eliminate H induced etching. Devices fabricated at 120 °C and 300 °C were compared.

Passivation of InGaAs(001)-(2 × 4) by Self-Limiting Chemical Vapor Deposition of a Silicon Hydride Control Layer.

A saturated Si-Hx seed layer for gate oxide or contact conductor ALD has been deposited via two separate self-limiting and saturating CVD processes on InGaAs(001)-(2 × 4) at substrate temperatures of 250 and 350 °C. For the first self-limiting process, a single silicon precursor, Si3H8, was dosed at a substrate temperature of 250 °C, and XPS results show the deposited silicon hydride layer saturated at about 4 monolayers of silicon coverage with hydrogen termination. STS results show the surface Fermi level remains unpinned following the deposition of the saturated silicon hydride layer, indicating the InGaAs surface dangling bonds are electrically passivated by Si-Hx. For the second self-limiting process, Si2Cl6 was dosed at a substrate temperature of 350 °C, and XPS results show the deposited silicon chloride layer saturated at about 2.5 monolayers of silicon coverage with chlorine termination. Atomic hydrogen produced by a thermal gas cracker was subsequently dosed at 350 °C to remove the Si-Cl termination by replacing with Si-H termination as confirmed by XPS, and STS results confirm the saturated Si-Hx bilayer leaves the InGaAs(001)-(2 × 4) surface Fermi level unpinned. Density function theory modeling of silicon hydride surface passivation shows an Si-Hx monolayer can remove all the dangling bonds and leave a charge balanced surface on InGaAs.

Dual passivation of intrinsic defects at the compound semiconductor/oxide interface using an oxidant and a reductant.

Studies have shown that metal oxide semiconductor field-effect transistors fabricated utilizing compound semiconductors as the channel are limited in their electrical performance. This is attributed to imperfections at the semiconductor/oxide interface which cause electronic trap states, resulting in inefficient modulation of the Fermi level. The physical origin of these states is still debated mainly because of the difficulty in assigning a particular electronic state to a specific physical defect. To gain insight into the exact source of the electronic trap states, density functional theory was employed to model the intrinsic physical defects on the InGaAs (2 × 4) surface and to model the effective passivation of these defects by utilizing both an oxidant and a reductant to eliminate metallic bonds and dangling-bond-induced strain at the interface. Scanning tunneling microscopy and spectroscopy were employed to experimentally determine the physical and electronic defects and to verify the effectiveness of dual passivation with an oxidant and a reductant. While subsurface chemisorption of oxidants on compound semiconductor substrates can be detrimental, it has been shown theoretically and experimentally that oxidants are critical to removing metallic defects at oxide/compound semiconductor interfaces present in nanoscale channels, oxides, and other nanostructures.

Atomic imaging of the irreversible sensing mechanism of NO2 adsorption on copper phthalocyanine.

Ambient NO2 adsorption onto copper(II) phthalocyanine (CuPc) monolayers is observed using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) to elucidate the molecular sensing mechanism in CuPc chemical vapor sensors. For low doses (1 ppm for 5 min) of NO2 at ambient temperatures, isolated chemisorption sites on the CuPc metal centers are observed in STM images. These chemisorbates almost completely desorb from the CuPc monolayer after annealing at 100 °C for 30 min. Conversely, for high NO2 doses (10 ppm for 5 min), the NO2 induces a fracture of the CuPc domains. This domain fracture can only be reversed by annealing above 150 °C, which is consistent with dissociative chemisorption into NO and atomic O accompanied by surface restructuring. This high stability implies that the domain fracture results from tightly bound adsorbates, such as atomic O. Existence of atomic O on or under the CuPc layer, which results in domain fracture, is revealed by XPS analysis and ozone-dosing experiments. The observed CuPc domain fracturing is consistent with a mechanism for the dosimetric sensing of NO2 and other reactive gases by CuPc organic thin film transistors (OTFTs).

Skin grafts provide durable end-bearing coverage for lower-extremity amputations with critical soft tissue loss.

Lower-extremity amputations in the presence of soft tissue loss represent an unresolved conundrum because surgeons must consider sacrificing bone length to obtain adequate soft tissue coverage. Local flaps and microvascular soft tissue transfers are established strategies for maintaining residual limb length. However, the use of skin grafts remains controversial due to the presumed inferiority compared with flaps with regard to enabling prosthetic fitting and full weight bearing. The current study was designed to test the hypothesis that split-thickness skin grafts represent a safe and feasible option to preserve bone length in lower-extremity amputations with critical soft tissue loss.

Dual passivation of GaAs (110) surfaces using O2/H2O and trimethylaluminum.

The nucleation and passivation of oxide deposition was studied on defect-free GaAs (110) surfaces to understand passivation of surfaces containing only III-V heterobonds. The passivation process on GaAs (110) was studied at the atomic level using scanning tunneling microscopy while the electronic structure was determined by scanning tunneling spectroscopy (STS). The bonding of the oxidant and reductant were modeled with density functional theory. To avoid Fermi level pinning during gate oxide atomic layer deposition, a dual passivation procedure was required using both a reductant, trimethylaluminum (TMA), and an oxidant, O2 or H2O. Dosing GaAs (110) with TMA resulted in the formation of an ordered complete monolayer of dimethylaluminum which passivates the group V dangling bonds but also forms metal-metal bonds with conduction band edge states. These edge states were suppressed by dosing the surface with oxidants O2 or H2O which selectively react with group III-aluminum bonds. The presence of an ordered Al monolayer with a high nucleation density was indirectly confirmed by XPS and STS.