Models for quantitative charge imaging by atomic force microscopy

Two models are presented for quantitative charge imaging with an atomic-force microscope. The first is appropriate for noncontact mode and the second for intermittent contact (tapping) mode imaging. Different forms for the contact force are used to demonstrate that quantitative charge imaging is possible without precise knowledge of the contact interaction. From the models, estimates of the best charge sensitivity of an unbiased standard atomic-force microscope cantilever are found to be on the order of a few electrons

Alien Registration- Bell, Marie Elizabeth A. (Van Buren, Aroostook County)

https://digitalmaine.com/alien_docs/33267/thumbnail.jp

Exotic Forest Insects and Residential Property Values

This paper presents a case study of the economic damages to homeowners in a northern New Jersey community due to an exotic forest insect--the hemlock woolly adelgid. Hedonic property value methods are used to estimate the effect of hemlock health on property values. A statistically significant relationship between hemlock health and residential property values is established. Moreover, there are some signs of spillover impacts from hemlock decline, as negative effects are realized on the parcels where the declining hemlock stands are located as well as on neighboring properties. These results give some indication of the benefits of potential control programs and strategies and also show support for community- or neighborhood-based programs in residential settings.invasive species, economic impacts, hedonic property values, general spatial model, Land Economics/Use,

Localized charge injection in SiO_2 films containing silicon nanocrystals

An atomic-force microscope (AFM) is used to locally inject, detect, and quantify the amount and location of charge in SiO2 films containing Si nanocrystals (size ~2–6 nm). By comparison with control samples, charge trapping is shown to be due to nanocrystals and not ion-implantation-induced defects in samples containing ion-beam-synthesized Si nanocrystals. Using an electrostatic model and AFM images of charge we have estimated the amount of charge injected in a typical experiment to be a few hundred electrons and the discharge rate to be ~35±15 e/min

Spatial and Electronic Manipulation of Silicon Nanocrystals by Atomic Force Microscopy

[As silicon-based devices shnnk, interest is increasing in fast, low-power devices sensitive to small numbers of electrons. Recent work suggests that MOS structures with large arrays of Si nanocrystals comprising a floating gate can be extremely fast, reliable and nonvolatile relative to conventional floating gate memories. In these structures approximately one electron is stored per nanocrystal. Despite promising initial results, current devices have a distribution of charge transit times during writing of nanocrystal ensembles, which limits speed. This behavior is not completely understood, but could be related to a dispersion in oxide thicknesses, nanocrystals interface states, or shifts in the electronic bound states due to size variations. To address these limitations, we have developed an aerosol vapor synthesis/deposition technique for silicon nanocrystals with active size classification, enabling narrow distributions of nanocrystal size (~10-15% of particle in the 2-10 nm size range). The first goal of these experiments has been to use scanning probe techniques to perform particle manipulation and to characterize particle electronic properties and charging on a single-particle basis. Si nanocrystal structures (lines, arrows and other objects) have been formed by contact-mode operation and subsequently imaged in noncontact mode without additional particle motion. Further, single nanocrystal charging by a conducting AFM tip has been observed, detected as an apparent height change due to electrostatic force, followed by a slow relaxation as the stored charge dissipates. Ongoing and future efforts will also be briefly discussed, including narrowing of nanocrystal size distributions, control of oxide thickness on the nanocrystals, and measurements of electron transport through individual particles and ensembles

Mental health and academic experiences among U.S. college students during the COVID-19 pandemic

When the COVID-19 pandemic began, U.S. college students reported increased anxiety and depression. This study examines mental health among U.S college students during the subsequent 2020–2021 academic year by surveying students at the end of the fall 2020 and the spring 2021 semesters. Our data provide cross-sectional snapshots and longitudinal changes. Both surveys included the PSS, GAD-7, PHQ-8, questions about students’ academic experiences and sense of belonging in online, in-person, and hybrid classes, and additional questions regarding behaviors, living circumstances, and demographics. The spring 2021 study included a larger, stratified sample of eight demographic groups, and we added scales to examine relationships between mental health and students’ perceptions of their universities’ COVID-19 policies. Our results show higher- than-normal frequencies of mental health struggles throughout the 2020–2021 academic year, and these were substantially higher for female college students, but by spring 2021, the levels did not vary substantially by race/ethnicity, living circumstances, vaccination status, or perceptions of university COVID-19 policies. Mental health struggles inversely correlated with scales of academic and non-academic experiences, but the struggles positively correlated with time on social media. In both semesters, students reported more positive experiences with in-person classes, though all class types were rated higher in the spring semester, indicating improvements in college students’ course experiences as the pandemic continued. Furthermore, our longitudinal data indicate the persistence of mental health struggles across semesters. Overall, these studies show factors that contributed to mental health challenges among college students as the pandemic continued

Antipodes Islands birds in autumn 2001

Abstract Observations of birds on Antipodes Islands during 24 April -6 June 2001 represent a season of the year for which data are lacking. Activity ashore of non-breeders of summer-breeding gadfly petrels Pterodroma spp. and blackbellied storm petrels (Fregetta tropica) continued until late May or even June. Data were obtained on the non-breeding behaviour, breeding cycle and burrow occupancy rates of grey petrels (Procellaria cinerea); only 50% of their burrows were occupied by breeding pairs. White-capped albatross (Thalassarche steadi) fledglings on Bollons Island were counted. There had been an autumnal immigration of some Passerines. Birds seen at sea on the voyages from Akaroa, Banks Peninsula and returning to Port Chalmers, Dunedin included the rarely-sighted Chatham taiko (Pterodroma magentae)

Alcohol intake and invasive breast cancer risk by molecular subtype and race in the Carolina Breast Cancer Study

Alcohol is an established breast cancer risk factor, but there is little evidence on whether the association differs between African Americans and whites

A Comparison of Network Sampling Designs for a Hidden Population of Drug Users: Random Walk vs. Respondent-Driven Sampling

Both random walk and respondent-driven sampling (RDS) exploit social networks and may reduce biases introduced by earlier methods for sampling from hidden populations. Although RDS has become much more widely used by social researchers than random walk (RW), there has been little discussion of the tradeoffs in choosing RDS over RW. This paper compares experiences of implementing RW and RDS to recruit drug users to a network-based study in Houston, Texas. Both recruitment methods were implemented over comparable periods of time, with the same population, by the same research staff. RDS methods recruited more participants with less strain on staff. However, participants recruited through RW were more forthcoming than RDS participants in helping to recruit members of their social networks. Findings indicate that, dependent upon study goals, researchers' choice of design may influence participant recruitment, participant commitment, and impact on staff, factors that may in turn affect overall study success