Imaging a Single-Electron Quantum Dot

Images of a single-electron quantum dot were obtained in the Coulomb blockade regime at liquid He temperatures using a cooled scanning probe microscope (SPM). The charged SPM tip shifts the lowest energy level in the dot and creates a ring in the image corresponding to a peak in the Coulomb-blockade conductance. Fits to the lineshape of the ring determine the tip-induced shift of the electron energy state in the dot. SPM manipulation of electrons in quantum dots promises to be useful in understanding, building and manipulating circuits for quantum information processing.Comment: 14 pages including 3 figure

Electric-field driven insulating to conducting transition in a mesoscopic quantum dot lattice

We investigate electron transport through a finite two dimensional mesoscopic periodic potential, consisting of an array of lateral quantum dots with electron density controlled by a global top gate. We observe a transition from an insulating state at low bias voltages to a conducting state at high bias voltages. The insulating state shows simply activated temperature dependence, with strongly gate voltage dependent activation energy. At low temperatures the transition between the insulating and conducting states becomes very abrupt and shows strong hysteresis. The high-bias behavior suggests underdamped transport through a periodic washboard potential resulting from collective motion.Comment: 4 pages, 4 figure

Localization and interaction of indirect excitons in GaAs coupled quantum wells

We introduced an elevated trap technique and exploited it for lowering the effective temperature of indirect excitons. We observed narrow photoluminescence lines which correspond to the emission of individual states of indirect excitons in a disorder potential. We studied the effect of exciton-exciton interaction on the localized and delocalized exciton states and found that the homogeneous line broadening increases with density and dominates the linewidth at high densities

Emergence of Clinical Clostridioides Difficile Isolates With Decreased Susceptibility to Vancomycin

BACKGROUND: Clostridioides difficile infection (CDI) is a leading cause of hospital-associated antibiotic-related diarrhea and deaths worldwide. Vancomycin is one of the few antibiotics recommended for both nonsevere and severe CDI cases. We sought to determine whether vancomycin nonsusceptible C. difficile strains are circulating in the patient population. METHODS: Stool samples from patients with CDI were collected from 438 and 98 patients at a large university hospital in Houston, Texas, and Nairobi, Kenya, respectively. The stools were examined for the presence of vancomycin and metronidazole nonsusceptible C. difficile using broth dilution culture, Etest (BioMérieux, France), polymerase chain reaction (PCR), whole-genome sequencing, and in vivo testing in a CDI mouse model. RESULTS: Of the Houston stool samples, 114/438 (26%) had vancomycin nonsusceptible C. difficile isolates and 128/438 (29%) were metronidazole nonsusceptible. Similarly, 66 out of 98 (67%) and 83/98 (85%) of the Nairobi patients harbored vancomycin and metronidazole nonsusceptible isolates, respectively. Vancomycin treatment of a CDI mouse model infected with a vancomycin nonsusceptible isolate failed to eradicate the infection. Whole-genome sequencing analyses did not identify vanA genes, suggesting a different mechanism of resistance. CONCLUSIONS: C. difficile strains exhibiting reduced susceptibility to vancomycin are currently circulating in patient populations. The spread of strains resistance to vancomycin, a first-line antibiotic for CDI, poses a serious therapeutic challenge. Routine susceptibility testing may be necessary

Defining Tobacco Regulatory Science Competencies

In 2013, the National Institutes of Health and the Food and Drug Administration funded a network of 14 Tobacco Centers of Regulatory Science (TCORS) with a mission that included research and training. A cross-TCORS Panel was established to define tobacco regulatory science (TRS) competencies to help harmonize and guide their emerging educational programs. The purpose of this paper is to describe the Panel’s work to develop core TRS domains and competencies

Defining Tobacco Regulatory Science Competencies

INTRODUCTION: In 2013, the National Institutes of Health and the Food and Drug Administration funded a network of 14 Tobacco Centers of Regulatory Science (TCORS) with a mission that included research and training. A cross-TCORS Panel was established to define tobacco regulatory science (TRS) competencies to help harmonize and guide their emerging educational programs. The purpose of this paper is to describe the Panel’s work to develop core TRS domains and competencies. METHODS: The Panel developed the list of domains and competencies using a semistructured Delphi method divided into four phases occurring between November 2013 and August 2015. RESULTS: The final proposed list included a total of 51 competencies across six core domains and 28 competencies across five specialized domains. CONCLUSIONS: There is a need for continued discussion to establish the utility of the proposed set of competencies for emerging TRS curricula and to identify the best strategies for incorporating these competencies into TRS training programs. Given the field’s broad multidisciplinary nature, further experience is needed to refine the core domains that should be covered in TRS training programs versus knowledge obtained in more specialized programs. IMPLICATIONS: Regulatory science to inform the regulation of tobacco products is an emerging field. The paper provides an initial list of core and specialized domains and competencies to be used in developing curricula for new and emerging training programs aimed at preparing a new cohort of scientists to conduct critical TRS research