3,864 research outputs found
Atom lithography using MRI-type feature placement
We demonstrate the use of frequency-encoded light masks in neutral atom
lithography. We demonstrate that multiple features can be patterned across a
monotonic potential gradient. Features as narrow as 0.9 microns are fabricated
on silicon substrates with a metastable argon beam. Internal state manipulation
with such a mask enables continuously adjustable feature positions and feature
densities not limited by the optical wavelength, unlike previous light masks.Comment: 4 pages, 4 figure
Experimental demonstration of a squeezing enhanced power recycled Michelson interferometer for gravitational wave detection
Interferometric gravitational wave detectors are expected to be limited by
shot noise at some frequencies. We experimentally demonstrate that a power
recycled Michelson with squeezed light injected into the dark port can overcome
this limit. An improvement in the signal-to-noise ratio of 2.3dB is measured
and locked stably for long periods of time. The configuration, control and
signal readout of our experiment are compatible with current gravitational wave
detector designs. We consider the application of our system to long baseline
interferometer designs such as LIGO.Comment: 4 pages 4 figure
Is Entrepreneurial Success Predictable? An Ex-Ante Analysis of the Character-Based Approach
This paper empirically analyzes whether the character-based approach, which focuses on the personality structure and the human capital of business founders, allows prediction of entrepreneurial success. A unique data set is used consisting of 414 persons whose personal characteristics were analyzed by different methods, namely an one-day assessment center (AC) and a standardized questionnaire, before they launched their business. Results are partly unexpected and weaker than previous ex-post findings: first, we found correlations between the AC data and the questionnaire in one subgroup only. Second, the predictive power of the AC data is slightly better than that of the questionnaire, but lower than expected in theory. Interestingly, for those subgroups where the AC data have low predictive power, the questionnaire does better. Third, when success is measured in terms of employees hired, the character-based approach is a poor predictor. Copyright 2008 The Authors.
Human Ό-calpain: Simple isolation from erythrocytes and characterization of autolysis fragments
Heterodimeric ÎŒ-calpain, consisting of the large (80 kDa) and the small (30 kDa) subunit, was isolated and purified from human erythrocytes by a highly reproducible four-step purification procedure. Obtained material is more than 95% pure and has a specific activity of 6 - 7 mU/mg. Presence of contaminating proteins could not be detected by HPLC and sequence analysis. During storage at -80 °C the enzyme remains fully activatable by CaÂČâș, although the small subunit is partially processed to a 22 kDa fragment. This novel autolysis product of the small subunit starts with the sequence (60)RILG and is further processed to the known 18 kDa fragment. Active forms and typical transient and stable autolysis products of the large subunit were identified by protein sequencing. In casein-zymograms only the activatable forms 80 kDa+30 kDa, 80 kDa+22 kDa and 80 kDa+18 kDa displayed caseinolysis
Atom focusing by far-detuned and resonant standing wave fields: Thin lens regime
The focusing of atoms interacting with both far-detuned and resonant standing
wave fields in the thin lens regime is considered. The thin lens approximation
is discussed quantitatively from a quantum perspective. Exact quantum
expressions for the Fourier components of the density (that include all
spherical aberration) are used to study the focusing numerically. The following
lens parameters and density profiles are calculated as functions of the pulsed
field area : the position of the focal plane, peak atomic density,
atomic density pattern at the focus, focal spot size, depth of focus, and
background density. The lens parameters are compared to asymptotic, analytical
results derived from a scalar diffraction theory for which spherical aberration
is small but non-negligible (). Within the diffraction theory
analytical expressions show that the focused atoms in the far detuned case have
an approximately constant background density
while the peak density behaves as , the focal distance or
time as , the focal spot size as
, and the depth of focus as .
Focusing by the resonant standing wave field leads to a new effect, a Rabi-
like oscillation of the atom density. For the far-detuned lens, chromatic
aberration is studied with the exact Fourier results. Similarly, the
degradation of the focus that results from angular divergence in beams or
thermal velocity distributions in traps is studied quantitatively with the
exact Fourier method and understood analytically using the asymptotic results.
Overall, we show that strong thin lens focusing is possible with modest laser
powers and with currently achievable atomic beam characteristics.Comment: 21 pages, 11 figure
Blue laser cooling transitions in Tm I
We have studied possible candidates for laser cooling transitions in
Tm in the spectral region 410 -- 420 nm. By means of saturation
absorption spectroscopy we have measured the hyperfine structure and rates of
two nearly closed cycling transitions from the ground state
to upper states
at
410.6 nm and
at
420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and
48(6) ns respectively. Decay rates from these levels to neighboring
opposite-parity levels are evaluated by means of Hartree-Fock calculations. We
conclude, that the strong transition at 410.6 nm has an optical leak rate of
less then and can be used for efficient laser cooling of
Tm from a thermal atomic beam. The hyperfine structure of two other
even-parity levels which can be excited from the ground state at 409.5 nm and
418.9 nm is also measured by the same technique. In addition we give a
calculated value of s for the rate of magnetic-dipole transition
at 1.14 m between the fine structure levels
of the ground state which can be
considered as a candidate for applications in atomic clocks.Comment: 8 pages, 5 figure
Quantum Noise Locking
Quantum optical states which have no coherent amplitude, such as squeezed
vacuum states, can not rely on standard readout techniques to generate error
signals for control of the quadrature phase. Here we investigate the use of
asymmetry in the quadrature variances to obtain a phase-sensitive readout and
to lock the phase of a squeezed vacuum state, a technique which we call noise
locking (NL). We carry out a theoretical derivation of the NL error signal and
the associated stability of the squeezed and anti-squeezed lock points.
Experimental data for the NL technique both in the presence and absence of
coherent fields are shown, including a comparison with coherent locking
techniques. Finally, we use NL to enable a stable readout of the squeezed
vacuum state on a homodyne detector.Comment: Accepted for publication in Journal of Optics:B special issue on
Quantum Contro
Analysis of the NGXO Telescope X-Ray Hartmann Data
Next Generation X-Ray Optics (NGXO) team at the Goddard Space Flight Center (GSFC) has been developing a new silicon-based grazing incidence mirror technology for future high resolution x-ray astronomical missions. Recently, the GSFC team completed the construction of first few mirror modules that contain one pair of mirrors. One of the mirror pairs was tested in GSFC 600-m long beamline facility and Panter (Neuried, Germay) 120-m long x-ray beamline facility. Both full aperture x-ray tests, Hartmann tests, and focal plane sweeps were completed. In this paper we present the data analysis process and compare the results from our models to measured x-ray centroid data, x-ray performance data, and out of focus images of the mirror pair
Talbot Oscillations and Periodic Focusing in a One-Dimensional Condensate
An exact theory for the density of a one-dimensional Bose-Einstein condensate
with hard core particle interactions is developed in second quantization and
applied to the scattering of the condensate by a spatially periodic impulse
potential. The boson problem is mapped onto a system of free fermions obeying
the Pauli exclusion principle to facilitate the calculation. The density
exhibits a spatial focusing of the probability density as well as a periodic
self-imaging in time, or Talbot effect. Furthermore, the transition from single
particle to many body effects can be measured by observing the decay of the
modulated condensate density pattern in time. The connection of these results
to classical and atom optical phase gratings is made explicit
Gravitational wave astronomy
The first decade of the new millenium should see the first direct detections
of gravitational waves. This will be a milestone for fundamental physics and it
will open the new observational science of gravitational wave astronomy. But
gravitational waves already play an important role in the modeling of
astrophysical systems. I review here the present state of gravitational
radiation theory in relativity and astrophysics, and I then look at the
development of detector sensitivity over the next decade, both on the ground
(such as LIGO) and in space (LISA). I review the sources of gravitational waves
that are likely to play an important role in observations by first- and
second-generation interferometers, including the astrophysical information that
will come from these observations. The review covers some 10 decades of
gravitational wave frequency, from the high-frequency normal modes of neutron
stars down to the lowest frequencies observable from space. The discussion of
sources includes recent developments regarding binary black holes, spinning
neutron stars, and the stochastic background.Comment: 29 pages, 2 figures, as submitted for special millenium issue of
Classical and Quantum Gravit
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