11,379 research outputs found
High-order optical nonlinearity at low light levels
We observe a nonlinear optical process in a gas of cold atoms that
simultaneously displays the largest reported fifth-order nonlinear
susceptibility \chi^(5) = 1.9x10^{-12} (m/V)^4 and high transparency. The
nonlinearity results from the simultaneous cooling and crystallization of the
gas, and gives rise to efficient Bragg scattering in the form of
six-wave-mixing at low-light-levels. For large atom-photon coupling strengths,
the back-action of the scattered fields influences the light-matter dynamics.
This system may have important applications in many-body physics, quantum
information processing, and multidimensional soliton formation.Comment: 5 pages, 3 figure
Total integrated dose testing of solid-state scientific CD4011, CD4013, and CD4060 devices by irradiation with CO-60 gamma rays
The total integrated dose response of three CMOS devices manufactured by Solid State Scientific has been measured using CO-60 gamma rays. Key parameter measurements were made and compared for each device type. The data show that the CD4011, CD4013, and CD4060 produced by this manufacturers should not be used in any environments where radiation levels might exceed 1,000 rad(Si)
Persistent organic pollutant burden, experimental POP exposure and tissue properties affect metabolic profiles of blubber from grey seal pups
Persistent organic pollutants (POPs) are toxic, ubiquitous, resist breakdown, bioaccumulate in living tissue and biomagnify in food webs. POPs can also alter energy balance in humans and wildlife. Marine mammals experience high POP concentrations, but consequences for their tissue metabolic characteristics are unknown. We used blubber explants from wild, grey seal (Halichoerus grypus) pups to examine impacts of intrinsic tissue POP burden and acute experimental POP exposure on adipose metabolic characteristics. Glucose use, lactate production and lipolytic rate differed between matched inner and outer blubber explants from the same individuals and between feeding and natural fasting. Glucose use decreased with blubber dioxin-like PCBs (DL-PCB) and increased with acute experimental POP exposure. Lactate production increased with DL-PCBs during feeding, but decreased with DL-PCBs during fasting. Lipolytic rate increased with blubber dichlorodiphenyltrichloroethane (DDT) and its metabolites (DDX) in fasting animals, but declined with DDX when animals were feeding. Our data show that POP burdens are high enough in seal pups to alter adipose function early in life, when fat deposition and mobilisation are vital. Such POP-induced alterations to adipose glucose use may significantly alter energy balance regulation in marine top predators with the potential for long term impacts on fitness and survival
Phase and micromotion of Bose-Einstein condensates in a time-averaged ring trap
Rapidly scanning magnetic and optical dipole traps have been widely utilised
to form time-averaged potentials for ultracold quantum gas experiments. Here we
theoretically and experimentally characterise the dynamic properties of
Bose-Einstein condensates in ring-shaped potentials that are formed by scanning
an optical dipole beam in a circular trajectory. We find that unidirectional
scanning leads to a non-trivial phase profile of the condensate that can be
approximated analytically using the concept of phase imprinting. While the
phase profile is not accessible through in-trap imaging, time-of-flight
expansion manifests clear density signatures of an in-trap phase step in the
condensate, coincident with the instantaneous position of the scanning beam.
The phase step remains significant even when scanning the beam at frequencies
two orders of magnitude larger than the characteristic frequency of the trap.
We map out the phase and density properties of the condensate in the scanning
trap, both experimentally and using numerical simulations, and find excellent
agreement. Furthermore, we demonstrate that bidirectional scanning eliminated
the phase gradient, rendering the system more suitable for coherent matter wave
interferometry.Comment: 10 pages, 7 figure
Evidence for spin liquid ground state in SrDyO frustrated magnet probed by muSR
Muon spin relaxation (SR) measurements were carried out on
SrDyO, a frustrated magnet featuring short range magnetic correlations
at low temperatures. Zero-field muon spin depolarization measurements
demonstrate that fast magnetic fluctuations are present from K down to
20 mK. The coexistence of short range magnetic correlations and fluctuations at
mK indicates that SrDyO features a spin liquid ground state.
Large longitudinal fields affect weakly the muon spin depolarization, also
suggesting the presence of fast fluctuations. For a longitudinal field of
T, a non-relaxing asymmetry contribution appears below K,
indicating considerable slowing down of the magnetic fluctuations as
field-induced magnetically-ordered phases are approached.Comment: 6 pages, 4 figures, to be published as a proceeding of HFM2016 in
Journal of Physics: Conference Series (JPCS
Branching Processes with Immigration and Integer-valued Time Series
In this paper, we indicate how integer-valued autoregressive time
series Ginar(d) of ordre d, d ≥ 1, are simple functionals of multitype branching
processes with immigration. This allows the derivation of a simple criteria for the
existence of a stationary distribution of the time series, thus proving and extending
some results by Al-Osh and Alzaid [1], Du and Li [9] and Gauthier and Latour
[11]. One can then transfer results on estimation in subcritical multitype branching
processes to stationary Ginar(d) and get consistency and asymptotic normality for
the corresponding estimators. The technique covers autoregressive moving average
time series as well
Transient dynamics and momentum redistribution in cold atoms via recoil-induced resonances
We use an optically dense, anisotropic magneto-optical trap to study
recoil-induced resonances (RIRs) in the transient, high-gain regime. We find
that two distinct mechanisms govern the atomic dynamics: the finite,
frequency-dependent atomic response time, and momentum-space population
redistribution. At low input probe intensities, the residual Doppler width of
the atoms, combined with the finite atomic response time, result in a linear,
transient hysteretic effect that modifies the locations, widths, and magnitudes
of the resulting gain spectra depending on the sign of the scan chirp. When
larger intensities (\textit{i.e.}, greater than a few W/cm) are
incident on the atomic sample for several s, hole-burning in the atomic
sample's momentum distribution leads to a coherent population redistribution
that persists for approximately 100 s. We propose using RIRs to engineer
the atomic momentum distribution to enhance the nonlinear atom-photon coupling.
We present a numerical model, and compare the calculated and experimental
results to verify our interpretation.Comment: 7 pages, 6 figure
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