2,280 research outputs found
Review of osteoimmunology and the host response in endodontic and periodontal lesions
Both lesions of endodontic origin and periodontal diseases involve the host response to bacteria and the formation of osteolytic lesions. Important for both is the upregulation of inflammatory cytokines that initiate and sustain the inflammatory response. Also important are chemokines that induce recruitment of leukocyte subsets and bone-resorptive factors that are largely produced by recruited inflammatory cells. However, there are differences also. Lesions of endodontic origin pose a particular challenge since that bacteria persist in a protected reservoir that is not readily accessible to the immune defenses. Thus, experiments in which the host response is inhibited in endodontic lesions tend to aggravate the formation of osteolytic lesions. In contrast, bacteria that invade the periodontium appear to be less problematic so that blocking arms of the host response tend to reduce the disease process. Interestingly, both lesions of endodontic origin and periodontitis exhibit inflammation that appears to inhibit bone formation. In periodontitis, the spatial location of the inflammation is likely to be important so that a host response that is restricted to a subepithelial space is associated with gingivitis, while a host response closer to bone is linked to bone resorption and periodontitis. However, the persistence of inflammation is also thought to be important in periodontitis since inflammation present during coupled bone formation may limit the capacity to repair the resorbed bone
Quenched Narrow-Line Laser Cooling of 40Ca to Near the Photon Recoil Limit
We present a cooling method that should be generally applicable to atoms with
narrow optical transitions. This technique uses velocity-selective pulses to
drive atoms towards a zero-velocity dark state and then quenches the excited
state to increase the cooling rate. We demonstrate this technique of quenched
narrow-line cooling by reducing the 1-D temperature of a sample of neutral 40Ca
atoms. We velocity select and cool with the 1S0(4s2) to 3P1(4s4p) 657 nm
intercombination line and quench with the 3P1(4s4p) to 1S0(4s5s)
intercombination line at 553 nm, which increases the cooling rate eight-fold.
Limited only by available quenching laser power, we have transferred 18 % of
the atoms from our initial 2 mK velocity distribution and achieved temperatures
as low as 4 microK, corresponding to a vrms of 2.8 cm/s or 2 recoils at 657 nm.
This cooling technique, which is closely related to Raman cooling, can be
extended to three dimensions.Comment: 5 pages, 4 figures; Submitted to PRA Rapid Communication
Observation and absolute frequency measurements of the 1S0 - 3P0 optical clock transition in ytterbium
We report the direct excitation of the highly forbidden (6s^2) 1S0 - (6s6p)
3P0 optical transition in two odd isotopes of ytterbium. As the excitation
laser frequency is scanned, absorption is detected by monitoring the depletion
from an atomic cloud at ~70 uK in a magneto-optical trap. The measured
frequency in 171Yb (F=1/2) is 518,295,836,593.2 +/- 4.4 kHz. The measured
frequency in 173Yb (F=5/2) is 518,294,576,850.0 +/- 4.4 kHz. Measurements are
made with a femtosecond-laser frequency comb calibrated by the NIST cesium
fountain clock and represent nearly a million-fold reduction in uncertainty.
The natural linewidth of these J=0 to J=0 transitions is calculated to be ~10
mHz, making them well-suited to support a new generation of optical atomic
clocks based on confinement in an optical lattice.Comment: 4 pages, 3 figure
Effect of Impurity Scattering on the Nonlinear Microwave Response in High-Tc Superconductors
We theoretically investigate intermodulation distortion in high-Tc
superconductors. We study the effect of nonmagnetic impurities on the real and
imaginary parts of nonlinear conductivity. The nonlinear conductivity is
proportional to the inverse of temperature owing to the dependence of the
damping effect on energy, which arises from the phase shift deviating from the
unitary limit. It is shown that the final-states interaction makes the real
part predominant over the imaginary part. These effects have not been included
in previous theories based on the two-fluid model, enabling a consistent
explanation for the experiments with the rf and dc fields
Multi-Wavelength Properties of the Type IIb SN 2008ax
We present the UV, optical, X-ray, and radio properties of the Type IIb SN
2008ax discovered in NGC 4490. The observations in the UV are one of the
earliest of a Type IIb supernova (SN). On approximately day four after the
explosion, a dramatic upturn in the u and uvw1 (lambda_c = 2600 Angstroms)
light curves occurred after an initial rapid decline which is attributed to
adiabatic cooling after the initial shock breakout. This rapid decline and
upturn is reminiscent of the Type IIb SN 1993J on day six after the explosion.
Optical/near-IR spectra taken around the peak reveal prominent H-alpha, HeI,
and CaII absorption lines. A fading X-ray source is also located at the
position of SN 2008ax, implying an interaction of the SN shock with the
surrounding circumstellar material and a mass-loss rate of the progenitor of
M_dot = (9+/-3)x10^-6 solar masses per year. The unusual time evolution (14
days) of the 6 cm peak radio luminosity provides further evidence that the
mass-loss rate is low. Combining the UV, optical, X-ray, and radio data with
models of helium exploding stars implies the progenitor of SN 2008ax was an
unmixed star in an interacting-binary. Modeling of the SN light curve suggests
a kinetic energy (E_k) of 0.5x10^51 ergs, an ejecta mass (M_ej) of 2.9 solar
masses, and a nickel mass (M_Ni) of 0.06 solar masses.Comment: Accepted to ApJ Letters, 14 pages, 3 figures, 2 table
The use and calibration of read-out streaks to increase the dynamic range of the Swift Ultraviolet/Optical Telescope
The dynamic range of photon counting micro-channel-plate (MCP) intensified
charged-coupled device (CCD) instruments such as the Swift Ultraviolet/Optical
Telescope (UVOT) and the XMM-Newton Optical Monitor (XMM-OM) is limited at the
bright end by coincidence loss, the superposition of multiple photons in the
individual frames recorded by the CCD. Photons which arrive during the brief
period in which the image frame is transferred for read out of the CCD are
displaced in the transfer direction in the recorded images. For sufficiently
bright sources, these displaced counts form read-out streaks. Using UVOT
observations of Tycho-2 stars, we investigate the use of these read-out streaks
to obtain photometry for sources which are too bright (and hence have too much
coincidence loss) for normal aperture photometry to be reliable. For
read-out-streak photometry, the bright-source limiting factor is coincidence
loss within the MCPs rather than the CCD. We find that photometric measurements
can be obtained for stars up to 2.4 magnitudes brighter than the usual
full-frame coincidence-loss limit by using the read-out streaks. The resulting
bright-limit Vega magnitudes in the UVOT passbands are UVW2=8.80, UVM2=8.27,
UVW1=8.86, u=9.76, b=10.53, v=9.31 and White=11.71; these limits are
independent of the windowing mode of the camera. We find that a photometric
precision of 0.1 mag can be achieved through read-out streak measurements. A
suitable method for the measurement of read-out streaks is described and all
necessary calibration factors are given.Comment: 11 pages, accepted for publication in MNRAS. Code available from the
calibration link at http://www.mssl.ucl.ac.uk/www_astro/uvo
A Statistical Comparison of the Optical/UV and X-ray Afterglows of Gamma-Ray Bursts using the Swift Ultra-violet Optical and X-ray Telescopes
We present the systematic analysis of the UVOT and XRT light curves for a
sample of 26 Swift Gamma-Ray Bursts (GRBs). By comparing the optical/UV and
X-ray light curves, we found that they are remarkably different during the
first 500s after the BAT trigger, while they become more similar during the
middle phase of the afterglow, i.e. between 2000s and 20000s. If we take
literally the average properties of the sample, we find that the mean temporal
indices observed in the optical/UV and X-rays after 500s are consistent with a
forward-shock scenario, under the assumptions that electrons are in the slow
cooling regime, the external medium is of constant density and the synchrotron
cooling frequency is situated between the optical/UV and X-ray observing bands.
While this scenario describes well the averaged observed properties, some
individual GRB afterglows require different or additional assumptions, such as
the presence of late energy injection. We show that a chromatic break (a break
in the X-ray light curve that is not seen in the optical) is present in the
afterglows of 3 GRBs and demonstrate evidence for chromatic breaks in a further
4 GRBs. The average properties of these breaks cannot be explained in terms of
the passage of the synchrotron cooling frequency through the observed bands,
nor a simple change in the external density. It is difficult to reconcile
chromatic breaks in terms of a single component outflow and instead, more
complex jet structure or additional emission components are required.Comment: 20 pages, 5 figures and 4 tables. Accepted for publication by MNRA
Doppler cooling and trapping on forbidden transitions
Ultracold atoms at temperatures close to the recoil limit have been achieved
by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms
has been cooled and trapped to a temperature as low as 6 \mu K by operating a
magneto-optical trap on the spin-forbidden intercombination transition.
Quenching the long-lived excited state with an additional laser enhanced the
scattering rate by a factor of 15, while a high selectivity in velocity was
preserved. With this method more than 10% of pre-cooled atoms from a standard
magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo
simulations of the cooling process are in good agreement with the experiments
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