6,113 research outputs found
Cosmic rays, solar activity, magnetic coupling, and lightning incidence
A theoretical model is presented and described that unifies the complex influence of several factors on spatial and temporal variation of lightning incidence. These factors include the cosmic radiation, solar activity, and coupling between geomagnetic and interplanetary (solar wind) magnetic fields. Atmospheric electrical conductivity in the 10 km region was shown to be the crucial parameter altered by these factors. The theory reconciles several large scale studies of lightning incidence previously misinterpreted or considered contradictory. The model predicts additional strong effects on variations in lightning incidence, but only small effects on the morphology and rate of thunderstorm development
Solar influence on terrestrial weather and global lightning patterns via cosmic ray modulations
A series of cosmic ray neutron monitor data which were used in three analyses: (1) solar activity influence on ionization of the upper troposphere and tropopause; (2) solar activity influence on Canadian high stratus in winter; and (3) the S3-4 satellite study of IMF/GMF magnetic coupling effects are reported. The magnetic coupling model of solar activity influence on atmospheric processes were investigated. The magnetic coupling model is used to explain a number of seemingly diverse studies lightning incidence is emphasized
The rise of an ionized wind in the Narrow Line Seyfert 1 Galaxy Mrk 335 observed by XMM-Newton and HST
We present the discovery of an outflowing ionized wind in the Seyfert 1
Galaxy Mrk 335. Despite having been extensively observed by most of the largest
X-ray observatories in the last decade, this bright source was not known to
host warm absorber gas until recent XMM-Newton observations in combination with
a long-term Swift monitoring program have shown extreme flux and spectral
variability. High resolution spectra obtained by the XMM-Newton RGS detector
reveal that the wind consists of three distinct ionization components, all
outflowing at a velocity of 5000 km/s. This wind is clearly revealed when the
source is observed at an intermediate flux state (2-5e-12 ergs cm^-2 s^-1). The
analysis of multi-epoch RGS spectra allowed us to compare the absorber
properties at three very different flux states of the source. No correlation
between the warm absorber variability and the X-ray flux has been determined.
The two higher ionization components of the gas may be consistent with
photoionization equilibrium, but we can exclude this for the only ionization
component that is consistently present in all flux states (log(xi)~1.8). We
have included archival, non-simultaneous UV data from HST (FOS, STIS, COS) with
the aim of searching for any signature of absorption in this source that so far
was known for being absorption-free in the UV band. In the COS spectra obtained
a few months after the X-ray observations we found broad absorption in CIV
lines intrinsic to the AGN and blueshifted by a velocity roughly comparable to
the X-ray outflow. The global behavior of the gas in both bands can be
explained by variation of the covering factor and/or column density, possibly
due to transverse motion of absorbing clouds moving out of the line of sight at
Broad Line Region scale.Comment: 24 pages, 12 figures, ApJ accepte
Just how hot are the Centauri extreme horizontal branch pulsators?
Past studies based on optical spectroscopy suggest that the five Cen
pulsators form a rather homogeneous group of hydrogen-rich subdwarf O stars
with effective temperatures of around 50 000 K. This places the stars below the
red edge of the theoretical instability strip in the log Teff diagram,
where no pulsation modes are predicted to be excited. Our goal is to determine
whether this temperature discrepancy is real, or whether the stars' effective
temperatures were simply underestimated. We present a spectral analysis of two
rapidly pulsating extreme horizontal branch (EHB) stars found in Cen.
We obtained Hubble Space Telescope/COS UV spectra of two Cen
pulsators, V1 and V5, and used the ionisation equilibrium of UV metallic lines
to better constrain their effective temperatures. As a by-product we also
obtained FUV lightcurves of the two pulsators. Using the relative strength of
the N IV and N V lines as a temperature indicator yields Teff values close to
60 000 K, significantly hotter than the temperatures previously derived. From
the FUV light curves we were able to confirm the main pulsation periods known
from optical data. With the UV spectra indicating higher effective temperatures
than previously assumed, the sdO stars would now be found within the predicted
instability strip. Such higher temperatures also provide consistent
spectroscopic masses for both the cool and hot EHB stars of our previously
studied sample.Comment: 9 pages, accepted for publication in Astronomy and Astrophysic
Direct catalytic conversion of cellulose to 5-hydroxymethylfurfural using ionic liquids
Cellulose is the single largest component of lignocellulosic biomass and is an attractive feedstock for a wide variety of renewable platform chemicals and biofuels, providing an alternative to petrochemicals and petrofuels. This potential is currently limited by the existing methods of transforming this poorly soluble polymer into useful chemical building blocks, such as 5-hydroxymethylfurfural (HMF). Ionic liquids have been used successfully to separate cellulose from the other components of lignocellulosic biomass and so the use of the same medium for the challenging transformation of cellulose into HMF would be highly attractive for the development of the biorefinery concept. In this report, ionic liquids based on 1-butyl-3-methylimidazolium cations [C4C1im]+ with Lewis basic (X = Cl−) and Brønsted acidic (X = HSO4−) anions were used to investigate the direct catalytic transformation of cellulose to HMF. Variables probed included the composition of the ionic liquid medium, the metal catalyst, and the reaction conditions (temperature, substrate concentration). Lowering the cellulose loading and optimising the temperature achieved a 58% HMF yield after only one hour at 150 °C using a 7 mol % loading of the CrCl3 catalyst. This compares favourably with current literature procedures requiring much longer reactions times or approaches that are difficult to scale such as microwave irradiation
Gamma radiation survey of the LDEF spacecraft
The retrieval of the Long Duration Exposure Facility spacecraft in January 1990 after nearly six years in orbit offered a unique opportunity to study the long term buildup of induced radioactivity in the variety of materials on board. We conducted the first complete gamma-ray survey of a large spacecraft on LDEF shortly after its return to earth. A surprising observation was the Be-7 activity which was seen primarily on the leading edge of the satellite, implying that it was picked up by LDEF in orbit. This is the first known evidence for accretion of a radioactive isotope onto an orbiting spacecraft. Other isotopes observed during the survey, the strongest being Na-22, are all attributed to activation of spacecraft components. Be-7 is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere. However, the observed density is much greater than expected due to cosmic-ray production in situ. This implies transport of Be-7 from much lower altitudes up to the LDEF orbit
Rotation as Contagion Mitigation
To prevent the spread of an infection an organization obeys social distancing restrictions and thus limits the number of its members physically present on a given day. We study rotation schemes in which mutually exclusive groups are active on different days. The frequency of rotation affects risk over the duration of diffusion prior to the time the organization is able to react to the infection. If this reaction time is speedy, then such risk is undesirable since prevalence is initially convex in time. In this case, frequent rotation acts as insurance against exposure-time risk and is optimal. Infrequent rotation becomes optimal if the organization reacts slowly. Cross-mixing of the rotating subpopulations is detrimental because it increases contacts between sick and healthy individuals. However, the effect of mixing is small if the terminal prevalence is low in the absence of mixing
Pilot Testing Behavior Therapy for Chronic Tic Disorders in Neurology and Developmental Pediatrics Clinics
Comprehensive Behavioral Intervention for Tics (CBIT) is an efficacious treatment with limited regional availability. As neurology and pediatric clinics are often the first point of therapeutic contact for individuals with tics, the present study assessed preliminary treatment response, acceptability, and feasibility of an abbreviated version, modified for child neurology and developmental pediatrics clinics. Fourteen youth (9-17) with Tourette disorder across 2 child neurology clinics and one developmental pediatrics clinic participated in a small case series. Clinician-rated tic severity (Yale Global Tic Severity Scale) decreased from pre- to posttreatment, z = –2.0, P \u3c .05, r = –.48, as did tic-related impairment, z = –2.4, P \u3c .05, r = –.57. Five of the 9 completers (56%) were classified as treatment responders. Satisfaction ratings were high, and therapeutic alliance ratings were moderately high. Results provide guidance for refinement of this modified CBIT protocol
The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?
Context. Radio-loud AGNs with powerful relativistic jets are thought to be
associated with rapidly spinning black holes (BHs). BH spin-up may result from
a number of processes, including accretion of matter onto the BH itself, and
catastrophic events such as BH-BH mergers. Aims. We study the intriguing
properties of the powerful (L_bol ~ 10^47 erg s^-1) radio-loud quasar 3C 186.
This object shows peculiar features both in the images and in the spectra.
Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the
properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical
spectra to study the kinematics of the source. Chandra X-ray data are also used
to better constrain the physical interpretation. Results. HST imaging shows
that the active nucleus is offset by 1.3 +- 0.1 arcsec (i.e. ~11 kpc) with
respect to the center of the host galaxy. Spectroscopic data show that the
broad emission lines are offset by -2140 +-390 km/s with respect to the narrow
lines. Velocity shifts are often seen in QSO spectra, in particular in
high-ionization broad emission lines. The host galaxy of the quasar displays a
distorted morphology with possible tidal features that are typical of the late
stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged
to account for the observed features. While the presence of a peculiar outflow
cannot be completely ruled out, all of the observed features are consistent
with those expected if the QSO is associated with a gravitational wave (GW)
recoiling BH. Future detailed studies of this object will allow us to confirm
this type of scenario and will enable a better understanding of both the
physics of BH-BH mergers and the phenomena associated with the emission of GW
from astrophysical sources.Comment: 16 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. New appendix adde
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