7,471 research outputs found
Self-pulsing dynamics in a cavity soliton laser
The dynamics of a broad-area vertical-cavity surface-emitting laser (VCSEL) with frequency-selective feedback supporting bistable spatial solitons is analyzed experimentally and theoretically. The transient dynamics of a switch-on of a soliton induced by an external optical pulse shows strong self-pulsing at the external-cavity round-trip time with at least ten modes excited. The numerical analysis indicates an even broader bandwidth and a transient sweep of the center frequency. It is argued that mode-locking of spatial solitons is an interesting and viable way to achieve three-dimensional, spatio-temporal self-localization and that the transients observed are preliminary indications of a transient cavity light bullet in the dynamics, though on a non negligible background
Blood lactate clearance during active recovery after an intense running bout depends on the intensity of the active recovery
High-intensity exercise training contributes to the production and accumulation of blood lactate, which is cleared by active recovery. However, there is no commonly agreed intensity or mode for clearing accumulated blood lactate. We studied clearance of accumulated blood lactate during recovery at various exercise intensities at or below the lactate threshold after high-intensity interval runs that prompted lactate accumulation. Ten males repeated 5-min running bouts at 90% of maximal oxygen uptake ([Vdot]O2max), which increased blood lactate concentration from 1.0 ± 0.1 to 3.9 ± 0.3 mmol · l-1. This was followed by recovery exercises ranging from 0 to 100% of lactate threshold. Repeated blood lactate measurements showed faster clearance of lactate during active versus passive recovery, and that the decrease in lactate was more rapid during higher (60-100% of lactate threshold) than lower (0-40% of lactate threshold) (P < 0.05) intensities. The more detailed curve and rate analyses showed that active recovery at 80-100% of lactate threshold had shorter time constants for 67% lactate clearance and higher peak clearance rates than 40% of lactate threshold or passive recovery (P < 0.05). Finally, examination of self-regulated intensities showed enhanced lactate clearance during higher versus lower intensities, further validating the intensity dependence of clearance of accumulated blood lactate. Therefore, active recovery after strenuous exercise clears accumulated blood lactate faster than passive recovery in an intensity-dependent manner. Maximum clearance occurred at active recovery close to the lactate threshold
A qualitative pilot study of food insecurity among Maasai women in Tanzania
Background: Food insecurity is an ongoing threat in rural sub-Saharan Africa and is complicated by cultural practices, the rise of chronicconditions such as HIV and land use availability. In order to develop a successful food security intervention program, it is important to be informed of the realities and needs of the target population. The purpose of this study was to pilot a qualitative method to understand food insecurity based on the lived experience of women of the Maasai population in the Ngorongoro Conservation Area of Tanzania.Methods: Short semi-structured qualitative interviews with 4 Maasai women.Results: Food insecurity was present in the Maasai community: the participants revealed that they did not always have access to safe and nutritious food that met the needs of themselves and their families. Themes that emerged from the data fell into three categories: Current practices (food sources, planning for enough, food preparation, and food preservation), food Insecurity (lack of food, emotions, coping strategies, and possible solutions), and division (co-wives, food distribution, and community relationships).Conclusion:This pilot study suggested the presence of food insecurity in the Maasai community. Larger sample studies are needed to clarify the extent and severity of food insecurity among this population. Having a detailed understanding of the various aspects of the food insecurity lived experience could inform a targeted intervention program.Key words: Food security, food supply, human rights, qualitative research, Eastern Afric
The Interaction between the ISM and Star Formation in the Dwarf Starburst Galaxy NGC 4214
We present the first interferometric study of the molecular gas in the
metal-poor dwarf starburst galaxy NGC 4214. Our map of the 12CO(1-0) emission,
obtained at the OVRO millimeter array, reveals an unexpected structural wealth.
We detected three regions of molecular emission in the north-west (NW),
south-east (SE) and centre of NGC 4214 which are in very different and distinct
evolutionary stages (total molecular mass: 5.1 x 10^6 M_sun). These differences
are apparent most dramatically when the CO morphologies are compared to optical
ground based and HST imaging: massive star formation has not started yet in the
NW region; the well-known starburst in the centre is the most evolved and star
formation in the SE complex started more recently. We derive a star formation
efficiency of 8% for the SE complex. Using high--resolution VLA observations of
neutral hydrogen HI and our CO data we generated a total gas column density map
for NGC 4214 (HI + H_2). No clear correlation is seen between the peaks of HI,
CO and the sites of ongoing star formation. This emphasizes the irregular
nature of dwarf galaxies. The HI and CO velocities agree well, so do the
H-alpha velocities. In total, we cataloged 14 molecular clumps in NGC 4214. Our
results from a virial mass analysis are compatible with a Galactic CO-to-H_2
conversion factor for NGC 4214 (lower than what is usually found in metal-poor
dwarf galaxies).Comment: accepted for publication in the AJ (February 2001), full ps file at:
ftp://ftp.astro.caltech.edu/users/fw/ngc4214/walter_prep.p
Frequency and phase locking of laser cavity solitons
Self-localized states or dissipative solitons have the freedom of translation in systems with a homogeneous background. When compared to cavity solitons in coherently driven nonlinear optical systems, laser cavity solitons have the additional freedom of the optical phase. We explore the consequences of this additional Goldstone mode and analyse experimentally and numerically frequency and phase locking of laser cavity solitons in a vertical-cavity surface-emitting laser with frequency-selective feedback. Due to growth-related variations of the cavity resonance, the translational symmetry is usually broken in real devices. Pinning to different defects means that separate laser cavity solitons have different frequencies and are mutually incoherent. If two solitons are close to each other, however, their interaction leads to synchronization due to phase and frequency locking with strong similarities to the Adler-scenario of coupled oscillators
Cooperative Jahn-Teller Distortion in PrO2
We report neutron diffraction data on single crystal PrO2 which reveal a
cooperative Jahn-Teller distortion at TD = 120 +/- 2 K. Below this temperature
an internal distortion of the oxygen sublattice causes the unit cell of the
crystallographic structure to become doubled along one crystal axis. We discuss
several possible models for this structure. The antiferromagnetic structure
below TN = 13.5 K is found to consist of two components, one of which shares
the same doubled unit cell as the distorted crystallographic structure. We also
present measurements of the magnetic susceptibility, the specific heat capacity
and the electrical conductivity of PrO2. The susceptibility data show an
anomaly at a temperature close to TD. From the specific heat capacity data we
deduce that the ground state is doubly degenerate, consistent with a distortion
of the cubic local symmetry. We discuss possible mechanisms for this. The
conductivity shows an activated behaviour with an activation energy Ea = 0.262
+/- 0.003 eV.Comment: 12 pages, 14 figures, 2 tables. Additional suggested structure in v
The Arecibo L-band Feed Array Zone of Avoidance Survey I: Precursor Observations through the Inner and Outer Galaxy
The Arecibo L-band Feed Array (ALFA) is being used to conduct a low-Galactic
latitude survey, to map the distribution of galaxies and large-scale structures
behind the Milky Way through detection of galaxies' neutral hydrogen (HI) 21-cm
emission. This Zone of Avoidance (ZOA) survey finds new HI galaxies which lie
hidden behind the Milky Way, and also provides redshifts for partially-obscured
galaxies known at other wavelengths. Before the commencement of the full
survey, two low-latitude precursor regions were observed, totalling 138 square
degrees, with 72 HI galaxies detected. Detections through the inner Galaxy
generally have no cataloged counterparts in any other waveband, due to the
heavy extinction and stellar confusion. Detections through the outer Galaxy are
more likely to have 2MASS counterparts. We present the results of these
precursor observations, including a catalog of the detected galaxies, with
their HI parameters. The survey sensitivity is well described by a flux- and
linewidth-dependent signal-to-noise ratio of 6.5. ALFA ZOA galaxies which also
have HI measurements in the literature show good agreement between our
measurements and previous work. The inner Galaxy precursor region was chosen to
overlap the HI Parkes Zone of Avoidance Survey so ALFA performance could be
quickly assessed. The outer Galaxy precursor region lies north of the Parkes
sky. Low-latitude large-scale structure in this region is revealed, including
an overdensity of galaxies near l = 183 deg and between 5000 - 6000 km/s in the
ZOA. The full ALFA ZOA survey will be conducted in two phases: a shallow survey
using the observing techniques of the precursor observations, and also a deep
phase with much longer integration time, with thousands of galaxies predicted
for the final catalog.Comment: 26 pages, 7 figures, 2 tables, Astronomical Journal accepte
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