1,252 research outputs found
Manipulation of a single charge in a double quantum dot
We manipulate a single electron in a fully tunable double quantum dot using
microwave excitation. Under resonant conditions, microwaves drive transitions
between the (1,0) and (0,1) charge states of the double dot. Local quantum
point contact charge detectors enable a direct measurement of the
photon-induced change in occupancy of the charge states. From charge sensing
measurements, we find T1~16 ns and a lower bound estimate for T2* of 400 ps for
the charge two-level system.Comment: related articles at http://marcuslab.harvard.ed
Electromagnetically Induced Transparency with an Ensemble of Donor-Bound Electron Spins in a Semiconductor
We present measurements of electromagnetically induced transparency with an
ensemble of donor- bound electrons in low-doped n-GaAs. We used optical
transitions from the Zeeman-split electron spin states to a bound trion state
in samples with optical densities of 0.3 and 1.0. The electron spin dephasing
time T* \approx 2 ns was limited by hyperfine coupling to fluctuating nuclear
spins. We also observe signatures of dynamical nuclear polarization, but find
these effects to be much weaker than in experiments that use electron spin
resonance and related experiments with quantum dots.Comment: 4 pages, 4 figures; Improved analysis of data in Fig. 3, corrected
factors of 2 and p
How Different Medical School Selection Processes Call upon Different Personality Characteristics
BACKGROUND:Research indicates that certain personality traits relate to performance in the medical profession. Yet, personality testing during selection seems ineffective. In this study, we examine the extent to which different medical school selection processes call upon desirable personality characteristics in applicants. METHODS:1019 of all 1055 students who entered the Dutch Bachelor of Medicine at University of Groningen, the Netherlands in 2009, 2010 and 2011 were included in this study. Students were admitted based on either top pre-university grades (n = 139), acceptance in a voluntary multifaceted selection process (n = 286), or lottery weighted for pre-university GPA. Within the lottery group, we distinguished between students who had not participated (n = 284) and students who were initially rejected (n = 310) in the voluntary selection process. Two months after admission, personality was assessed with the NEO-FFI, a measure of the five factor model of personality. We performed ANCOVA modelling with gender as a covariate to examine personality differences between the four groups. RESULTS:The multifaceted selection group scored higher on extraversion than all other groups(p<0.01), higher on conscientiousness than both lottery-admitted groups(p<0.01), and lower on neuroticism than the lottery-admitted group that had not participated in the voluntary selection process. The latter group scored lower on conscientiousness than all other groups(p<0.05) and lower on agreeableness than the multifaceted selection group and the top pre-university group(p<0.01). CONCLUSIONS:Differences between the four admission groups, though statistically significant, were relatively small. Personality scores in the group admitted through the voluntary multifaceted selection process seemed most fit for the medical profession. Personality scores in the lottery-admitted group that had not participated in this process seemed least fit for the medical profession. It seems that in order to select applicants with suitable personalities, an admission process that calls upon desirable personality characteristics is beneficial
The conceptual design of SeamFrame
This project deliverable provides the underlying architecture of a concept for linking models and databases and it provides the design of SeamFrame, delivering its architecture to provide an integration framework for models and simulation algorithms, supported by procedures for data handling and spatial representation, quality control, output visualization and documentatio
Entanglement between charge qubits induced by a common dissipative environment
We study entanglement generation between two charge qubits due to the strong
coupling with a common bosonic environment (Ohmic bath). The coupling to the
boson bath is a source of both quantum noise (leading to decoherence) and an
indirect interaction between qubits. As a result, two effects compete as a
function of the coupling strength with the bath: entanglement generation and
charge localization induced by the bath. These two competing effects lead to a
non-monotonic behavior of the concurrence as a function of the coupling
strength with the bath. As an application, we present results for charge qubits
based on double quantum dots.Comment: 9 pages, 7 figure
Interference effects in isolated Josephson junction arrays with geometric symmetries
As the size of a Josephson junction is reduced, charging effects become
important and the superconducting phase across the link turns into a periodic
quantum variable. Isolated Josephson junction arrays are described in terms of
such periodic quantum variables and thus exhibit pronounced quantum
interference effects arising from paths with different winding numbers
(Aharonov-Casher effects). These interference effects have strong implications
for the excitation spectrum of the array which are relevant in applications of
superconducting junction arrays for quantum computing. The interference effects
are most pronounced in arrays composed of identical junctions and possessing
geometric symmetries; they may be controlled by either external gate potentials
or by adding/removing charge to/from the array. Here we consider a loop of N
identical junctions encircling one half superconducting quantum of magnetic
flux. In this system, the ground state is found to be non-degenerate if the
total number of Cooper pairs on the array is divisible by N, and doubly
degenerate otherwise (after the stray charges are compensated by the gate
voltages).Comment: 9 pages, 6 figure
Biophysical Modeling of Mangrove Seedling Establishment and Survival Across an Elevation Gradient With Forest Zones
Mangrove forest development critically depends on the establishment and survival of seedlings. Mechanistic insights into how water levels, waves and bed level dynamics influence the establishment process of individual mangrove seedlings are increasing. However, little is known about how spatial and temporal changes in water levels, waves and bed level dynamics across elevation gradients in mangrove forests facilitate/limit seedling dynamics. For this study, a new seedling establishment and growth model was integrated into a process-based hydrodynamic and morphodynamic numerical model. This biophysical model was applied to a fringing mangrove forest located in the southern Firth of Thames, Aotearoa, New Zealand. This study quantifies the increasing establishment density and survival probability of mangrove seedlings from the lower-elevated unvegetated intertidal flat toward the higher-elevated mature mangrove forest. Three cross-shore zones with distinctive seedling dynamics were identified: (a) a zone with daily tidal inundation where seedling dynamics are episodic and limited by the dispersal of individual propagules that rapidly anchor to the substrate by root growth, (b) a zone with daily to bi-weekly tidal inundation where seedling dynamics respond to variations in spring-neap tidal cycles and, (c) a zone with less than bi-weekly inundation where seedling dynamics are governed by high propagule supply and seedling survival probability. The seedling establishment density and survival probability are dominated by annual extremes in tidal hydroperiod and bed shear stresses, respectively. The obtained parameterizations can be used to incorporate seedling dynamics in decadal-timescale mangrove forest development models that are instrumental for mangrove management and restoration
Highly abundant HCN in the inner hot envelope of GL 2591: probing the birth of a hot core?
We present observations of the v2=0 and vibrationally excited v2=1 J=9-8
rotational lines of HCN at 797 GHz toward the deeply embedded massive young
stellar object GL 2591, which provide the missing link between the extended
envelope traced by lower-J line emission and the small region of hot (T_ex >=
300 K), abundant HCN seen in 14 micron absorption with the Infrared Space
Observatory (ISO). The line ratio yields T_ex=720^+135_-100 K and the line
profiles reveal that the hot gas seen with ISO is at the velocity of the
protostar, arguing against a location in the outflow or in shocks. Radiative
transfer calculations using a depth-dependent density and temperature structure
show that the data rule out a constant abundance throughout the envelope, but
that a model with a jump of the abundance in the inner part by two orders of
magnitude matches the observations. Such a jump is consistent with the sharp
increase in HCN abundance at temperatures >~230 K predicted by recent chemical
models in which atomic oxygen is driven into water at these temperatures.
Together with the evidence for ice evaporation in this source, this result
suggests that we may be witnessing the birth of a hot core. Thus, GL 2591 may
represent a rare class of objects at an evolutionary stage just preceding the
`hot core' stage of massive star formation.Comment: Accepted by ApJ Letters, 11 pages including 3 figures, uses AASTe
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