Surface Modifications Of Silicon Induced By Low Energy Reactive Ion Bombardment

The effects of low energy reactive ion bombardment of semiconducting silicon material have been investigated by X-ray photoelectron spectroscopy. The residual surface damage induced by a conventional fluorocarbon plasma reactive ion etching of silicon consisted of a uniform fluorocarbon deposited film approximately 4nm in thickness which covered a silicon compound reaction layer. This reaction layer was comprised of silicon oxides, carbide and fluorosilyl species distributed in depth to approximately 2nm. The removal of the residuel surface damage was accomplished by an ozone oxidation plus a wet oxide chemical etching step processing and monitored by surface charge spectroscopy. This residual surface damage to silicon was simulated by mass-filtered reactive F{dollar}\sp+{dollar}, and CF{dollar}\sp+{dollar} ion beam bombardment of silicon at normal incidence and room temperature. In addition, the effects of Cl{dollar}\sp+{dollar} ion beam bombardment of silicon were studied in order to provide fundamental information on the chlorine plasma dry etching. The ion kinetic energy range of interest was 1eV to 100eV for ion doses between {dollar}3\times 10\sp{lcub}14{rcub}{dollar} and {dollar}1\times 10\sp{lcub}18{rcub}{dollar}/cm{dollar}\sp2{dollar}. The residual surface damage to the silicon was seen as surface incorporation of the reactive ion species in the form of a fluorosilyl species layer for F{dollar}\sp+{dollar} bombardment, a fluorocarbon deposited layer and a silicon carbide/fluorosilyl layer for CF{dollar}\sp+{dollar} bombardment, and finally, surface oxidation and subsequent sputtering of the oxygenated species by Cl{dollar}\sp+{dollar} bombardment. The surface species of SiX{dollar}\sb{lcub}\rm n{rcub}{dollar} with X = F or Cl, and for n ranging from 1 to 4 were different for the two halogen ions investigated. For Cl{dollar}\sp+{dollar} bombardment, n was less than 2 for the ion energy range of 1 to 100eV, while for F{dollar}\sp+{dollar} ions, n included 1 to 4. Distinct surface reaction products were consistent with the reactivity of the specific ion/silicon systems

LDEF polymeric materials: 10 months versus 5.8 years of exposure

The chemical characterization of several polymeric materials which received 10 months of exposure and 5.8 years of exposure on a Row 9 Long Duration Exposure Facility (LDEF) experiment (A0134) is reported. Specimens include fluorinated ethylene propylene (FEP) teflon film, polysulfone film, and graphite fiber reinforced epoxy amd polysulfone matrix composites. The responses of these materials to the two LEO exposures are compared. The results of infrared, thermal, x-ray photoelectron, and scanning electron microscope analyses are reported. Solution property measurements of various molecular weight parameters are presented for the thermoplastic polysulfone materials. Molecular level effects attributable to exposure that were present in 10-month exposed specimens were not found in 5.8-year exposed specimens. This result suggests that increased atomic oxygen fluence toward the end of the LDEF mission may have eroded away selected environmentally induced changes in surface chemistry for 5.8-year exposure specimens

Cooperation between NRF-2 and YY-1 transcription factors is essential for triggering the expression of the PREPL-C2ORF34 bidirectional gene pair

<p>Abstract</p> <p>Background</p> <p>Many mammalian genes are organized as bidirectional (head-to-head) gene pairs with the two genes separated only by less than 1 kb. The transcriptional regulation of these bidirectional gene pairs remains largely unclear, but a few studies have suggested that the two closely adjacent genes in divergent orientation can be co-regulated by a single transcription factor binding to a specific regulatory fragment. Here we report an evolutionarily conserved bidirectional gene pair, known as the <it>PREPL-C2ORF34 </it>gene pair, whose transcription relies on the synergic cooperation of two transcription factors binding to an intergenic bidirectional minimal promoter.</p> <p>Results</p> <p>While <it>PREPL </it>is present primarily in brain and heart, <it>C2ORF34 </it>is ubiquitously and abundantly expressed in almost all tissues. Genomic analyses revealed that these two non-homologous genes are adjacent in a head-to-head configuration on human chromosome 2p21 and separated by only 405 bp. Within this short intergenic region, a 243-bp GC-rich segment was demonstrated to function as a bidirectional minimal promoter to initiate the transcription of both flanking genes. Two key transcription factors, NRF-2 and YY-1, were further identified to coordinately participate in driving both gene expressions in an additive manner. The functional cooperation between these two transcription factors, along with their genomic binding sites and some cis-acting repressive elements, are essential for the transcriptional activation and tissue distribution of the <it>PREPL-C2ORF34 </it>bidirectional gene pair.</p> <p>Conclusion</p> <p>This study provides new insights into the complex transcriptional mechanism of a mammalian head-to-head gene pair which requires cooperative binding of multiple transcription factors to a bidirectional minimal promoter of the shared intergenic region.</p

A Global Perspective of Business Usage of Web Technology

Despite the recent downturn in Internet and telecommunication sectors, e-commerce is forecasted to continue to grow and corporate websites have remained as important communication channels for both businesses and consumers. However, many multi-nation corporations (MNCs) use the same business websites for their business transactions in all of their business locations, even across national boundaries. Does this kind of “one website fits all” mentality of using Web technology really work well in reality? Does national culture matter in terms of influencing the adopting of Web technology for commercial usage in MNCs? Whether corporations in different countries/cultures use Web technology differently in their commercial websites? This paper intends to explore the above important research issues through examining and comparing the usage of commercial websites among corporations in two different countries: Singapore and the United States

THE INVISIBLE MOATS OF THE MUN RIVER VALLEY, NE THAILAND: THE EXAMINATION OF WATER MANAGEMENT DEVICES AT MOUNDED SITES THROUGH GROUND PENETRATING RADAR (GPR)

The Mun River valley is well known for its moat-bound mounded archaeological sites that are usually associated with Iron Age occupation (~500BC- AD500).  The investigation of these sites has provided a wealth of information on the changing social and environmental conditions during prehistory.  In recent years, research has identified a greater diversity of site morphologies in the region, many of which, importantly, do not appear to have moats surrounding them.  This paper seeks to investigate whether the apparently ‘non-moated’ mound site of Non Klang (Nong Hua Raet village) was actually moated in the past, and if such, now in-filled features can be investigated through non-destructive Ground Penetrating Radar methodology.  Additionally, while large external moats can be observed in the modern day topography at sites such as Ban Non Wat, excavation has demonstrated that further, invisible, water management features exist beneath the surface within the current mound boundary of the site.  These are probably Iron Age precursors to the later more extensive and still visible moats.  This paper seeks to answer several fundamental questions: What application can GPR have at mounded sites in Southeast Asia?  Do invisible moats exist?  How will this affect our understanding of the broader prehistoric landscape in the Upper Mun River Valley? 

Academic Achievement of English Language Learners in Post Proposition 203 Arizona

Improvements in school accountability labels received by public elementary schools in Arizona fail to convey the decline in English Language Learner (ELL) test scores. Test data reveal that large achievement gaps still exist between ELLs and their counterparts, and that Structured English Immersion–the state's mandated method for teaching ELLs after the passage of Proposition 203–has not resulted in increased achievement

Layer 3 pyramidal neurons of rhesus monkeys in aging and after ischemic injury

Layer 3 (L3) pyramidal neurons are involved in intrinsic and extrinsic corticocortical communications that are integral to area specific cortical functions. The functional and morphological properties of these neurons are altered in the lateral prefrontal cortex (LPFC) of aged rhesus monkeys, changes which parallel the decline of working memory (WM) function. What is not yet understood is the time course of these neuronal alternations during the aging process, or the impact of neuronal changes on the function of local networks that underlie WM. By comparing the properties of L3 pyramidal neurons from the LPFC of behaviorally characterized rhesus monkeys over the adult lifespan using whole cell patch clamp recordings and neuronal reconstructions, the present dissertation demonstrates that WM impairment, neuronal hyperexcitabilty and spine loss begin in middle age. We use bump attractor models to predict how empirically observed changes affect performance on the Delayed Response Task and Delayed Recognition Span Task (spatial). The performance of both models is affected much more by neuronal hyperexcitability than by synapse loss. In a separate study, we examine pathological changes of L3 pyramidal neurons in the perilesional ventral premotor cortex following acute ischemic injury to the primary motor cortex. Neurons from lesioned monkeys exhibit hyperexcitability and changes the excitatory:inhibitory synaptic balance in favor of inhibition. As oxidative stress and inflammation are known to exacerbate both age-related and injury-induced neuronal pathology, we characterize neuronal properties in both conditions after administering therapeutic interventions which target inflammatory pathways and which have previously been shown to ameliorate behavioral deficits. Chronic dietary curcumin treatment dampens neuronal hyperexcitability in middle-aged subjects, but the neuronal changes are not correlated with WM improvements. Treatment with mesenchymal-derived extracellular vesicles lowers firing rates and restores excitatory:inhibitory synaptic balance, and importantly, these changes correlate significantly with motor function