Evolution of Iron Kα_{\alpha} Line Emission in the Black Hole Candidate GX 339-4

GX 339-4 was regularly monitored with RXTE during a period (in 1999) when its X-ray flux decreased significantly (from 4.2$\times 10^{-10}$ erg cm$^{-2} s^{-1}$ to 7.6$\times 10^{-12}$ erg cm$^{-2}$s$^{-1}$ in the 3--20 keV band), as the source settled into the ``off state''. Our spectral analysis revealed the presence of a prominent iron K$_{\alpha}$ line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at $\sim$6.4 keV when the measured flux is above 5$\times 10^{-11}$ erg cm$^{-2} s^{-1}$, but is shifted to $\sim$6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism, because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to recombination cascade of hydrogen or helium like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.Comment: 18 pages, 2 figures, accepted for publication in the ApJ in v552n2p May 10, 2001 issu

LHC Searches for Non-Chiral Weakly Charged Multiplets

Because the TeV-scale to be probed at the Large Hadron Collider should shed light on the naturalness, hierarchy, and dark matter problems, most searches to date have focused on new physics signatures motivated by possible solutions to these puzzles. In this paper, we consider some candidates for new states that although not well-motivated from this standpoint are obvious possibilities that current search strategies would miss. In particular we consider vector representations of fermions in multiplets of $SU(2)_L$ with a lightest neutral state. Standard search strategies would fail to find such particles because of the expected small one-loop-level splitting between charged and neutral states.Comment: 16 pages, 9 figure

Field-effect transistors assembled from functionalized carbon nanotubes

We have fabricated field effect transistors from carbon nanotubes using a novel selective placement scheme. We use carbon nanotubes that are covalently bound to molecules containing hydroxamic acid functionality. The functionalized nanotubes bind strongly to basic metal oxide surfaces, but not to silicon dioxide. Upon annealing, the functionalization is removed, restoring the electronic properties of the nanotubes. The devices we have fabricated show excellent electrical characteristics.Comment: 5 pages, 6 figure

Emulating advanced neural functions with spin textures for neuromorphic computing

Neuromorphic computing calls for devices that exhibit intrinsic neuronal functions for compact, energy efficient hardware implementations. Spintronic devices allow for electrical or magnetic control of the spin polarization of the computing media and are gaining importance in neuromorphic computing due to benefits in endurance, energy efficiency and CMOS processing compatibility. Most importantly, their reconfigurable spin textures provide additional flexibility in mimicking the complex, dynamic behaviors of the biological neurons and synapses. This dissertation explores the mapping of neuronal functions onto spin textures within ferromagnetic thin films, particularly focusing on domain walls (DW) and skyrmions. Through a combination of device modeling and experimental studies, I aim to demonstrate that the manipulability of these spin textures holds significant promise for neuromorphic computing applications. I will introduce the fundamental concepts of magnetism and magnetic materials that lay the groundwork for understanding DW and skyrmion dynamics. The integrated DW-magnetic tunnel junction (MTJ) device is first discussed as a basis for spintronic neuromorphic applications. Device-level micromagnetic modeling reveals the mechanism behind the intrinsic lateral inhibition (LI) phenomena between DW-MTJ integrate-fire neurons, and I will show the methodology to maximize LI, which is essential for regulating neuronal activities and facilitating winner-take-all (WTA) functions. A novel adaptive neuron is designed by leveraging the rich dynamics of skyrmions to emulate advanced cognitive functions such as adaptive responses and cross-frequency coupling (CFC). Device functionality is validated using micromagnetic modeling, and their superiority in context-aware learning is demonstrated through neural network modeling. The experimental study focuses on the design and fabrication of a DW-MTJ integrate-fire neuron device which improves the DW injection and reset characteristics of previous implementations. Fabrication techniques and optimization are presented, along with experimental demonstration of device functionality. I highlight the future integration of neuron and synapse devices into a monolithic, all-spintronic neuromorphic network, paving the way for stream learning applications. Overall, this dissertation contributes to advancing the application of spintronic devices in neuromorphic computing, offering insights into the potential of spin textures for next-generation cognitive computing systems.Electrical and Computer Engineerin

Combinations of β-lactam or aminoglycoside antibiotics with plectasin are synergistic against methicillin-sensitive and methicillin-resistant Staphylococcus aureus.

Bacterial infections remain the leading killer worldwide which is worsened by the continuous emergence of antibiotic resistance. In particular, methicillin-sensitive (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) are prevalent and the latter can be difficult to treat. The traditional strategy of novel therapeutic drug development inevitably leads to emergence of resistant strains, rendering the new drugs ineffective. Therefore, rejuvenating the therapeutic potentials of existing antibiotics offers an attractive novel strategy. Plectasin, a defensin antimicrobial peptide, potentiates the activities of other antibiotics such as β-lactams, aminoglycosides and glycopeptides against MSSA and MRSA. We performed in vitro and in vivo investigations to test against genetically diverse clinical isolates of MSSA (n = 101) and MRSA (n = 115). Minimum inhibitory concentrations (MIC) were determined by the broth microdilution method. The effects of combining plectasin with β-lactams, aminoglycosides and glycopeptides were examined using the chequerboard method and time kill curves. A murine neutropenic thigh model and a murine peritoneal infection model were used to test the effect of combination in vivo. Determined by factional inhibitory concentration index (FICI), plectasin in combination with aminoglycosides (gentamicin, neomycin or amikacin) displayed synergistic effects in 76-78% of MSSA and MRSA. A similar synergistic response was observed when plectasin was combined with β-lactams (penicillin, amoxicillin or flucloxacillin) in 87-89% of MSSA and MRSA. Interestingly, no such interaction was observed when plectasin was paired with vancomycin. Time kill analysis also demonstrated significant synergistic activities when plectasin was combined with amoxicillin, gentamicin or neomycin. In the murine models, plectasin at doses as low as 8 mg/kg augmented the activities of amoxicillin and gentamicin in successful treatment of MSSA and MRSA infections. We demonstrated that plectasin strongly rejuvenates the therapeutic potencies of existing antibiotics in vitro and in vivo. This is a novel strategy that can have major clinical implications in our fight against bacterial infections

Essays on public finance and health economics

This dissertation examines several questions in public finance, including health care, workers' compensation program, and tax rebates. The first chapter, entitled, "Financial Incentives and Physicians’ Behavior: Evidence from Texas Workers’ Compensation Medical Claims", examines whether financial incentives influence the quantity and composition of medical care provided by physicians. I study this question by leveraging an administrative change in the maximum allowed reimbursement rates for surgical services performed in a hospital setting for Texas Workers' Compensation medical claims. I document evidence of strong substitution in the location of care, indicating that many surgical services can be provided in either a hospital or office setting. I find that the 2% increase in surgical services provided in a hospital setting in response to this reform is fully offset by reduced utilization in an office setting. I also find that nonsurgical services performed in a hospital increased in response to the reform, suggesting surgical and nonsurgical services are complements with respect to physician financial incentives. More generally, my results suggest that the location of care is responsive to financial incentives, and an optimal payment policy should account for substitution along this margin. The second chapter, entitled "Cash-on-Hand and Demand for Credit", examines the effect of tax rebates on demand for small dollar credit loans. Subprime consumers often use small dollar credit to meet short-term financial needs over pay cycles. However, relatively little is known about the income sensitivity of demand for credit in this market. This chapter provides a causal estimate of the effect of tax rebates on the demand for small dollar credit, using shocks from the Earned Income Tax Credit (EITC) benefits and a unique proprietary loan-level dataset. The results show that a $100 increase in EITC benefits leads to a 8.3% in the number of loan applications and a 6.6% reduction in the number of borrowers. This could translate into sizable reductions in loan volume and savings in financial charges. The estimates are robust to various specifications checks. The results further indicate that EITC recipients are liquidity constrained. More broadly, the results suggest that public programs with income benefits could help recipients with consumption smoothing in the presence of credit market frictions. The third chapter, entitled "Take-up of Workers' Compensation Insurance in Texas", is coauthored with Marika Cabral and Michael Dworsky. This chapter examines how employers choose to provide benefits for their workers. Workers' compensation program is a large government program which provides monetary and medical benefits to injured workers. Texas is currently the only state that allows voluntary participation. Using difference-in-differences variation in regulated manual premium, this paper empirically analyzes employers' take-up of workers' compensation insurance coverage. We find that 10% increase in regulated premium reduces the number of covered firms by 2%, with similar effect on covered payroll.Economic

Regulation of ABCC6 trafficking and stability by a conserved C-terminal PDZ-like sequence

Mutations in the ABCC6 ABC-transporter are causative of pseudoxanthoma elasticum (PXE). The loss of functional ABCC6 protein in the basolateral membrane of the kidney and liver is putatively associated with altered secretion of a circulatory factor. As a result, systemic changes in elastic tissues are caused by progressive mineralization and degradation of elastic fibers. Premature arteriosclerosis, loss of skin and vascular tone, and a progressive loss of vision result from this ectopic mineralization. However, the identity of the circulatory factor and the specific role of ABCC6 in disease pathophysiology are not known. Though recessive loss-of-function alleles are associated with alterations in ABCC6 expression and function, the molecular pathologies associated with the majority of PXE-causing mutations are also not known. Sequence analysis of orthologous ABCC6 proteins indicates the C-terminal sequences are highly conserved and share high similarity to the PDZ sequences found in other ABCC subfamily members. Genetic testing of PXE patients suggests that at least one disease-causing mutation is located in a PDZ-like sequence at the extreme C-terminus of the ABCC6 protein. To evaluate the role of this C-terminal sequence in the biosynthesis and trafficking of ABCC6, a series of mutations were utilized to probe changes in ABCC6 biosynthesis, membrane stability and turnover. Removal of this PDZ-like sequence resulted in decreased steady-state ABCC6 levels, decreased cell surface expression and stability, and mislocalization of the ABCC6 protein in polarized cells. These data suggest that the conserved, PDZ-like sequence promotes the proper biosynthesis and trafficking of the ABCC6 protein. © 2014 Xue et al

Suppression of MAPK11 or HIPK3 reduces mutant Huntingtin levels in Huntington's disease models.

Most neurodegenerative disorders are associated with accumulation of disease-relevant proteins. Among them, Huntington disease (HD) is of particular interest because of its monogenetic nature. HD is mainly caused by cytotoxicity of the defective protein encoded by the mutant Huntingtin gene (HTT). Thus, lowering mutant HTT protein (mHTT) levels would be a promising treatment strategy for HD. Here we report two kinases HIPK3 and MAPK11 as positive modulators of mHTT levels both in cells and in vivo. Both kinases regulate mHTT via their kinase activities, suggesting that inhibiting these kinases may have therapeutic values. Interestingly, their effects on HTT levels are mHTT-dependent, providing a feedback mechanism in which mHTT enhances its own level thus contributing to mHTT accumulation and disease progression. Importantly, knockout of MAPK11 significantly rescues disease-relevant behavioral phenotypes in a knockin HD mouse model. Collectively, our data reveal new therapeutic entry points for HD and target-discovery approaches for similar diseases

Pacing and Decision Making in Sport and Exercise: The Roles of Perception and Action in the Regulation of Exercise Intensity

In pursuit of optimal performance, athletes and physical exercisers alike have to make decisions about how and when to invest their energy. The process of pacing has been associated with the goal-directed regulation of exercise intensity across an exercise bout. The current review explores divergent views on understanding underlying mechanisms of decision making in pacing. Current pacing literature provides a wide range of aspects that might be involved in the determination of an athlete's pacing strategy, but lacks in explaining how perception and action are coupled in establishing behaviour. In contrast, decision-making literature rooted in the understanding that perception and action are coupled provides refreshing perspectives on explaining the mechanisms that underlie natural interactive behaviour. Contrary to the assumption of behaviour that is managed by a higher-order governor that passively constructs internal representations of the world, an ecological approach is considered. According to this approach, knowledge is rooted in the direct experience of meaningful environmental objects and events in individual environmental processes. To assist a neuropsychological explanation of decision making in exercise regulation, the relevance of the affordance competition hypothesis is explored. By considering pacing as a behavioural expression of continuous decision making, new insights on underlying mechanisms in pacing and optimal performance can be developed. © 2014 Springer International Publishing Switzerland

Wetlands for wastewater treatment and subsequent recycling of treated effluent : a review

Due to water scarcity challenges around the world, it is essential to think about non-conventional water resources to address the increased demand in clean freshwater. Environmental and public health problems may result from insufficient provision of sanitation and wastewater disposal facilities. Because of this, wastewater treatment and recycling methods will be vital to provide sufficient freshwater in the coming decades, since water resources are limited and more than 70% of water are consumed for irrigation purposes. Therefore, the application of treated wastewater for agricultural irrigation has much potential, especially when incorporating the reuse of nutrients like nitrogen and phosphorous, which are essential for plant production. Among the current treatment technologies applied in urban wastewater reuse for irrigation, wetlands were concluded to be the one of the most suitable ones in terms of pollutant removal and have advantages due to both low maintenance costs and required energy. Wetland behavior and efficiency concerning wastewater treatment is mainly linked to macrophyte composition, substrate, hydrology, surface loading rate, influent feeding mode, microorganism availability, and temperature. Constructed wetlands are very effective in removing organics and suspended solids, whereas the removal of nitrogen is relatively low, but could be improved by using a combination of various types of constructed wetlands meeting the irrigation reuse standards. The removal of phosphorus is usually low, unless special media with high sorption capacity are used. Pathogen removal from wetland effluent to meet irrigation reuse standards is a challenge unless supplementary lagoons or hybrid wetland systems are used