897 research outputs found
Directional takeoff, aerial righting, and adhesion landing of semiaquatic springtails
Springtails (Collembola) have been traditionally portrayed as explosive
jumpers with incipient directional takeoff and uncontrolled landing. However,
for these collembolans who live near the water, such skills are crucial for
evading a host of voracious aquatic and terrestrial predators. We discover that
semiaquatic springtails Isotomurus retardatus can perform directional jumps,
rapid aerial righting, and near-perfect landing on the water surface. They
achieve these locomotive controls by adjusting their body attitude and impulse
during takeoff, deforming their body in mid-air, and exploiting the
hydrophilicity of their ventral tube, known as collophore. Experiments and
mathematical modeling indicate that directional-impulse control during takeoff
is driven by the collophores adhesion force, the body angle, and the stroke
duration produced by their jumping organ, the furcula. In mid-air, springtails
curve their bodies to form a U-shape pose, which leverages aerodynamic forces
to right themselves in less than 20 ms, the fastest ever measured in animals. A
stable equilibrium is facilitated by the water adhered to the collophore.
Aerial righting was confirmed by placing springtails in a vertical wind tunnel
and through physical models. Due to these aerial responses, springtails land on
their ventral side 85% of the time while anchoring via the collophore on the
water surface to avoid bouncing. We validated the springtail biophysical
principles in a bioinspired jumping robot that reduces in-flight rotation and
lands upright 75% of the time. Thus, contrary to common belief, these wingless
hexapods can jump, skydive and land with outstanding control that can be
fundamental for survival.Comment: 12 pages, 8 figure
The Association between Drought Exposure and Respiratory-Related Mortality in the United States from 2000 to 2018
Climate change has brought increasing attention to the assessment of health risks associated with climate and extreme events. Drought is a complex climate phenomenon that has been increasing in frequency and severity both locally and globally due to climate change. However, the health risks of drought are often overlooked, especially in places such as the United States, as the pathways to health impacts are complex and indirect. This study aims to conduct a comprehensive assessment of the effects of monthly drought exposure on respiratory mortality for NOAA climate regions in the United States from 2000 to 2018. A two-stage model was applied to estimate the location-specific and overall effects of respiratory risk associated with two different drought indices over two timescales (the US Drought Monitor and the 6-month and 12-month Evaporative Demand Drought Index). During moderate and severe drought exposure, respiratory mortality risk ratio in the general population increased up to 6.0% (95% Cr: 4.8 to 7.2) in the Northeast, 9.0% (95% Cr: 4.9 to 13.3) in the Northern Rockies and Plains, 5.2% (95% Cr: 3.9 to 6.5) in the Ohio Valley, 3.5% (95% Cr: 1.9 to 5.0) in the Southeast, and 15.9% (95% Cr: 10.8 to 20.4) in the Upper Midwest. Our results showed that age, ethnicity, sex (both male and female), and urbanicity (both metro and non-metro) resulted in more affected population subgroups in certain climate regions. The magnitude and direction of respiratory risk ratio differed across NOAA climate regions. These results demonstrate a need for policymakers and communities to develop more effective strategies to mitigate the effects of drought across regions
Three Millisecond Pulsars in FERMI LAT Unassociated Bright Sources
We searched for radio pulsars in 25 of the non-variable, unassociated sources
in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz.
We report the discovery of three radio and gamma-ray millisecond pulsars (MSPs)
from a high Galactic latitude subset of these sources. All of the pulsars are
in binary systems, which would have made them virtually impossible to detect in
blind gamma-ray pulsation searches. They seem to be relatively normal, nearby
(<=2 kpc) millisecond pulsars. These observations, in combination with the
Fermi detection of gamma-rays from other known radio MSPs, imply that most, if
not all, radio MSPs are efficient gamma-ray producers. The gamma-ray spectra of
the pulsars are power-law in nature with exponential cutoffs at a few GeV, as
has been found with most other pulsars. The MSPs have all been detected as
X-ray point sources. Their soft X-ray luminosities of ~10^{30-31} erg/s are
typical of the rare radio MSPs seen in X-rays.Comment: Accepted for publication in ApJ Letter
Recommended from our members
Synthesis of Prussian blue-embedded porous polymer for detection and removal of Cs ions
A Prussian blue (PB)â-âembedded coordination polymer (COP) was prepd. by simple incorporation of PB into a COP composed of 1,â1,â2,â2-âtetrakis(4-âcarboxyphenyl)âethane and the Zn ion during the synthesis of COP. The PB-âCOP was prepd. as micro-âsized particles with green emission (490 nm) from the strongly fluorescent tetraphenylethene group in the solid state through aggregation-âinduced emission. The PB-âCOP showed particle shape with sizes ranging from 1 to 6 ÎŒm. As the PB in PB-âCOP efficiently adsorbed Cs ions, the microstructure of PB-âCOP was degraded to smaller particles, along with a concomitant decrease in the green fluorescence of the PB-âCOP. Such a decrease in the green emission of PB-âCOP was used as a signal for the presence of Cs ions, in which the limit of detection for Cs ions was found to be 73.8 ppb. The hybridized material of the PB-âCOP can be used as both an efficient adsorbent and a sensor for Cs ions, achieving simultaneous removal and detection
AXTAR: Mission Design Concept
The Advanced X-ray Timing Array (AXTAR) is a mission concept for X-ray timing
of compact objects that combines very large collecting area, broadband spectral
coverage, high time resolution, highly flexible scheduling, and an ability to
respond promptly to time-critical targets of opportunity. It is optimized for
submillisecond timing of bright Galactic X-ray sources in order to study
phenomena at the natural time scales of neutron star surfaces and black hole
event horizons, thus probing the physics of ultradense matter, strongly curved
spacetimes, and intense magnetic fields. AXTAR's main instrument, the Large
Area Timing Array (LATA) is a collimated instrument with 2-50 keV coverage and
over 3 square meters effective area. The LATA is made up of an array of
supermodules that house 2-mm thick silicon pixel detectors. AXTAR will provide
a significant improvement in effective area (a factor of 7 at 4 keV and a
factor of 36 at 30 keV) over the RXTE PCA. AXTAR will also carry a sensitive
Sky Monitor (SM) that acts as a trigger for pointed observations of X-ray
transients in addition to providing high duty cycle monitoring of the X-ray
sky. We review the science goals and technical concept for AXTAR and present
results from a preliminary mission design study.Comment: 19 pages, 10 figures, to be published in Space Telescopes and
Instrumentation 2010: Ultraviolet to Gamma Ray, Proceedings of SPIE Volume
773
Eight gamma-ray pulsars discovered in blind frequency searches of Fermi LAT data
We report the discovery of eight gamma-ray pulsars in blind frequency
searches using the LAT, onboard the Fermi Gamma-ray Space Telescope. Five of
the eight pulsars are young (tau_c10^36 erg/s), and
located within the Galactic plane (|b|<3 deg). The remaining three are older,
less energetic, and located off the plane. Five pulsars are associated with
sources included in the LAT bright gamma-ray source list, but only one, PSR
J1413-6205, is clearly associated with an EGRET source. PSR J1023-5746 has the
smallest characteristic age (tau_c=4.6 kyr) and is the most energetic
(Edot=1.1E37 erg/s) of all gamma-ray pulsars discovered so far in blind
searches. PSRs J1957+5033 and J2055+25 have the largest characteristic ages
(tau_c~1 Myr) and are the least energetic (Edot~5E33 erg/s) of the
newly-discovered pulsars. We present the timing models, light curves, and
detailed spectral parameters of the new pulsars. We used recent XMM
observations to identify the counterpart of PSR J2055+25 as XMMU
J205549.4+253959. In addition, publicly available archival Chandra X-ray data
allowed us to identify the likely counterpart of PSR J1023-5746 as a faint,
highly absorbed source, CXOU J102302.8-574606. The large X-ray absorption
indicates that this could be among the most distant gamma-ray pulsars detected
so far. PSR J1023-5746 is positionally coincident with the TeV source HESS
J1023-575, located near the young stellar cluster Westerlund 2, while PSR
J1954+2836 is coincident with a 4.3 sigma excess reported by Milagro at a
median energy of 35 TeV. Deep radio follow-up observations of the eight pulsars
resulted in no detections of pulsations and upper limits comparable to the
faintest known radio pulsars, indicating that these can be included among the
growing population of radio-quiet pulsars in our Galaxy being uncovered by the
LAT, and currently numbering more than 20.Comment: Submitted to Ap
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