107 research outputs found
The Volatile Composition of the Split Ecliptic comet 73P/Schwassmann-Wachmann 3: A Comparison of Fragments C and B
The composition of fragments C and B of the Jupiter-family comet 73P/Schwassmann-Wachmann 3 (SW3) was investigated in early April of 2006 at IR wavelengths using high-dispersion echelle spectroscopy. Both fragments were depleted in ethane, and C was depleted in most forms of volatile carbon. In particular, fragment C shows a severe depletion of CH_(3)OH but a "normal" abundance of HCN (which has a similar volatility). Thermal processing is a possible explanation, but since fragment B is perhaps sublimating fresher material because of the frequent outbursts and fragmentation, the observed depletions might have cosmogonic implications. The chemistry of the volatile ices in SW3, like in the Oort Cloud comet C/1999 S4 (LINEAR), may be associated with sublimation of icy mantles from precometary grains followed by subsequent gas-phase chemistry and recondensation
Comet C/2004 Q2 (MACHHOLZ): Parent Volatiles, a Search for Deuterated Methane, and Constraint on the CH4 Spin Temperature
High-dispersion (l/dl ~ 25,000) infrared spectra of Comet C/2004 Q2
(Machholz) were acquired on Nov. 28-29, 2004, and Jan. 19, 2005 (UT dates) with
NIRSPEC at the Keck-2 telescope on Mauna Kea. We detected H2O, CH4, C2H2, C2H6,
CO, H2CO, CH3OH, HCN, and NH3 and we conducted a sensitive search for CH3D. We
report rotational temperatures, production rates, and mixing ratios (with
respect to H2O) at heliocentric distances of 1.49 AU (Nov. 2004) and 1.21 AU
(Jan. 2005). We highlight three principal results: (1) The mixing ratios of
parent volatiles measured at 1.49 AU and 1.21 AU agree within confidence
limits, consistent with homogeneous composition in the mean volatile release
from the nucleus of C/2004 Q2. Notably, the relative abundance of C2H6/C2H2 is
substantially higher than those measured in other comets, while the mixing
ratios C2H6/H2O, CH3OH/H2O, and HCN/H2O are similar to those observed in
comets, referred to as "organics-normal". (2) The spin temperature of CH4 is >
35-38 K, an estimate consistent with the more robust spin temperature found for
H2O. (3) We obtained a 3s upper limit of CH3D/CH4 < 0.020 (D/H < 0.005). This
limit suggests that methane released from the nucleus of C/2004 Q2 is not
dominated by a component formed in extremely cold (near 10 K) environments.
Formation pathways of both interstellar and nebular origin consistent with the
measured D/H in methane are discussed. Evaluating the relative contributions of
these pathways requires further modeling of chemistry including both gas-phase
and gas-grain processes in the natal interstellar cloud and in the
protoplanetary disk.Comment: Accepted by The Astrophysical Journa
A Search for Variation in the H_2O Ortho-Para Ratio and Rotational Temperature in the Inner Coma of Comet C/2004 Q2 (Machholz)
We present spatially resolved measurements of the rotational temperature and ortho-para ratio for H_2O in the inner coma of the Oort Cloud comet C/2004 Q2 (Machholz). Our results are based on direct simultaneous detections of ortho-H_2O and para-H_2O via "hot-band" fluorescence near 2.9 μm. We find a well-defined decline in rotational temperature with increasing nucleocentric distance (up to ~1000 km). The ortho-para ratio remains constant (within stochastic uncertainty) with increasing nucleocentric distance and is close to the statistical equilibrium value of 3.0 (2.86 ± 0.06 [0.17], including, respectively, stochastic [systematic] uncertainty), resulting in spin temperature T_(spin) ≥ 34 K. We compare the present results with those reported for other comets and discuss the difficulties in interpreting spin temperatures deduced from measured ortho-para ratios. Improved understanding of the special conditions that enable nuclear spin conversion would test the extent to which derived spin temperatures reflect the formative history or the processing record of cometary ices
Spin Damping in an RF Atomic Magnetometer
Under negative feedback, the quality factor Q of a radio-frequency
magnetometer can be decreased by more than two orders of magnitude, so that any
initial perturbation of the polarized spin system can be rapidly damped,
preparing the magnetometer for detection of the desired signal. We find that
noise is also suppressed under such spin-damping, with a characteristic
spectral response corresponding to the type of noise; therefore magnetic,
photon-shot, and spin-projection noise can be measured distinctly. While the
suppression of resonant photon-shot noise implies the closed-loop production of
polarization-squeezed light, the suppression of resonant spin-projection noise
does not imply spin-squeezing, rather simply the broadening of the noise
spectrum with Q. Furthermore, the application of spin-damping during
phase-sensitive detection suppresses both signal and noise in such a way as to
increase the sensitivity bandwidth. We demonstrate a three-fold increase in the
magnetometer's bandwidth while maintaining 0.3 fT/\surdHz sensitivity.Comment: 24 pages, 7 figure
Suppression of type 1 pilus assembly in uropathogenic Escherichia coli by chemical inhibition of subunit polymerization
OBJECTIVES:
To identify and to characterize small-molecule inhibitors that target the subunit polymerization of the type 1 pilus assembly in uropathogenic Escherichia coli (UPEC).
METHODS:
Using an SDS-PAGE-based assay, in silico pre-filtered small-molecule compounds were screened for specific inhibitory activity against the critical subunit polymerization step of the chaperone-usher pathway during pilus biogenesis. The biological activity of one of the compounds was validated in assays monitoring UPEC type 1 pilus biogenesis, type 1 pilus-dependent biofilm formation and adherence to human bladder epithelial cells. The time dependence of the in vivo inhibitory activity and the overall effect of the compound on UPEC growth were determined.
RESULTS:
N-(4-chloro-phenyl)-2-{5-[4-(pyrrolidine-1-sulfonyl)-phenyl]-[1,3,4]oxadiazol-2-yl sulfanyl}-acetamide (AL1) inhibited in vitro pilus subunit polymerization. In bacterial cultures, AL1 disrupted UPEC type 1 pilus biogenesis and pilus-dependent biofilm formation, and resulted in the reduction of bacterial adherence to human bladder epithelial cells, without affecting bacterial cell growth. Bacterial exposure to the inhibitor led to an almost instantaneous loss of type 1 pili.
CONCLUSIONS:
We have identified and characterized a small molecule that interferes with the assembly of type 1 pili. The molecule targets the polymerization step during the subunit incorporation cycle of the chaperone-usher pathway. Our discovery provides new insight into the design and development of novel anti-virulence therapies targeting key virulence factors of bacterial pathogens
Parent Volatiles in Comet 9P/Tempel 1: Before and After Impact
We quantified eight parent volatiles (H_2O, C_2H_6, HCN, CO, CH_3OH, H_2CO, C_2H_2, and CH_4) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk
High-resolution X-ray spectroscopy of rare events: a different look at local structure and chemistry
The combination of large-acceptance high-resolution X-ray optics with bright synchrotron sources permits quantitative analysis of rare events such as X-ray fluorescence from very dilute systems, weak fluorescence transitions or X-ray Raman scattering. Transition-metal Kβ fluorescence contains information about spin and oxidation state; examples of the characterization of the Mn oxidation states in the oxygen-evolving complex of photosystem II and Mn-consuming spores from the marine bacillus SG-1 are presented. Weaker features of the Kβ spectrum resulting from valence-level and 'interatomic' ligand to metal transitions contain detailed information on the ligand-atom type, distance and orientation. Applications of this spectral region to characterize the local structure of model compounds are presented. X-ray Raman scattering (XRS) is an extremely rare event, but also represents a unique technique to obtain bulk-sensitive low-energy
Sprouted Innervation into Uterine Transplants Contributes to the Development of Hyperalgesia in a Rat Model of Endometriosis
Endometriosis is an enigmatic painful disorder whose pain symptoms remain difficult to alleviate in large part because the disorder is defined by extrauteral endometrial growths whose contribution to pain is poorly understood. A rat model (ENDO) involves autotransplanting on abdominal arteries uterine segments that grow into vascularized cysts that become innervated with sensory and sympathetic fibers. ENDO rats exhibit vaginal hyperalgesia. We used behavioral, physiological, and immunohistochemical methods to test the hypothesis that cyst innervation contributes to the development of this hyperalgesia after transplant. Rudimentary sensory and sympathetic innervation appeared in the cysts at two weeks, sprouted further and more densely into the cyst wall by four weeks, and matured by six weeks post-transplant. Sensory fibers became abnormally functionally active between two and three weeks post-transplant, remaining active thereafter. Vaginal hyperalgesia became significant between four and five weeks post-transplant, and stabilized after six to eight weeks. Removing cysts before they acquired functional innervation prevented vaginal hyperalgesia from developing, whereas sham cyst removal did not. Thus, abnormally-active innervation of ectopic growths occurs before hyperalgesia develops, supporting the hypothesis. These findings suggest that painful endometriosis can be classified as a mixed inflammatory/neuropathic pain condition, which opens new avenues for pain relief. The findings also have implications beyond endometriosis by suggesting that functionality of any transplanted tissue can be influenced by the innervation it acquires
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