589 research outputs found
GOES dynamic propagation of attitude
The spacecraft in the next series of Geostationary Operational Environmental Satellites (GOES-Next) are Earth pointing and have 5-year mission lifetimes. Because gyros can be depended on only for a few years of continuous use, they will be turned off during routine operations. This means attitude must, at times, be determined without benefit of gyros and, often, using only Earth sensor data. To minimize the interruption caused by dumping angular momentum, these spacecraft have been designed to reduce the environmental torque acting on them and incorporate an adjustable solar trim tab for fine adjustment. A new support requirement for GOES-Next is that of setting the solar trim tab. Optimizing its setting requires an estimate of the unbalanced torque on the spacecraft. These two requirements, determining attitude without gyros and estimating the external torque, are addressed by replacing or supplementing the gyro propagation with a dynamic one, that is, one that integrates the rigid body equations of motion. By processing quarter-orbit or longer batches, this approach takes advantage of roll-yaw coupling to observe attitude completely without Sun sensor data. Telemetered momentum wheel speeds are used as observations of the unbalanced external torques. GOES-Next provides a unique opportunity to study dynamic attitude propagation. The geosynchronous altitude and adjustable trim tab minimize the external torque and its uncertainty, making long-term dynamic propagation feasible. This paper presents the equations for dynamic propagation, an analysis of the environmental torques, and an estimate of the accuracies obtainable with the proposed method
Dynamics and stability of Bose-Einstein solitons in tilted optical lattices
Bloch oscillations of Bose-Einstein condensates realize sensitive matter-wave
interferometers. We investigate the dynamics and stability of bright-soliton
wave packets in one-dimensional tilted optical lattices with a modulated
mean-field interaction . By means of a time-reversal argument, we prove
the stability of Bloch oscillations of breathing solitons that would be
quasistatically unstable. Floquet theory shows that these breathing solitons
can be more stable against certain experimental perturbations than rigid
solitons or even non-interacting wave packets.Comment: final, published versio
Stability and decay of Bloch oscillations in presence of time-dependent nonlinearity
We consider Bloch oscillations of Bose-Einstein condensates in presence of a
time-modulated s-wave scattering length. Generically, interaction leads to
dephasing and decay of the wave packet. Based on a cyclic-time argument, we
find---additionally to the linear Bloch oscillation and a rigid soliton
solution---an infinite family of modulations that lead to a periodic time
evolution of the wave packet. In order to quantitatively describe the dynamics
of Bloch oscillations in presence of time-modulated interactions, we employ two
complementary methods: collective-coordinates and the linear stability analysis
of an extended wave packet. We provide instructive examples and address the
question of robustness against external perturbations.Comment: 15 pages, 8 figures. Slightly amended final versio
Nuclear Magnetic Resonance Studies of the Structure and Binding Sites of Enzymes, XII. A Conformational Equilibrium in Staphylococcal Nuclease Involving a Histidine Residue
Effects of circadian rhythm phase alteration on physiological and psychological variables: Implications to pilot performance (including a partially annotated bibliography)
The effects of environmental synchronizers upon circadian rhythmic stability in man and the deleterious alterations in performance and which result from changes in this stability are points of interest in a review of selected literature published between 1972 and 1980. A total of 2,084 references relevant to pilot performance and circadian phase alteration are cited and arranged in the following categories: (1) human performance, with focus on the effects of sleep loss or disturbance and fatigue; (2) phase shift in which ground based light/dark alteration and transmeridian flight studies are discussed; (3) shiftwork; (4)internal desynchronization which includes the effect of evironmental factors on rhythmic stability, and of rhythm disturbances on sleep and psychopathology; (5) chronotherapy, the application of methods to ameliorate desynchronization symptomatology; and (6) biorythm theory, in which the birthdate based biorythm method for predicting aircraft accident susceptability is critically analyzed. Annotations are provided for most citations
An NMR structural study of nickel-substituted rubredoxin
J Biol Inorg Chem (2010) 15:409–420
DOI 10.1007/s00775-009-0613-6The Ni(II) and Zn(II) derivatives of Desulfovibrio vulgaris rubredoxin (DvRd) have been studied by NMR spectroscopy to probe the structure at the metal centre. The βCH2 proton pairs from the cysteines that bind the Ni(II) atom have been identified using 1D nuclear Overhauser enhancement (NOE) difference spectra and sequence specifically assigned via NOE correlations to neighbouring protons and by comparison with the published X-ray crystal structure of a Ni(II) derivative of Clostridium pasteurianum rubredoxin. The solution structures of DvRd(Zn) and DvRd(Ni) have been determined and the paramagnetic form refined using pseudocontact shifts. The determination of the magnetic susceptibility anisotropy tensor allowed the contact and pseudocontact contributions to the observed chemical shifts to be obtained. Analysis of the pseudocontact and contact chemical shifts of the cysteine Hβ protons and backbone protons close to the metal centre allowed conclusions to be drawn as to the geometry and hydrogen-bonding pattern at the metal binding site. The importance of NH–S hydrogen bonds at the metal centre for the delocalization of electron spin density is confirmed for rubredoxins and can be extrapolated to metal centres in Cu proteins: amicyanin, plastocyanin, stellacyanin, azurin and pseudoazurin
Cluster headache with ptosis responsive to intranasal lidocaine application: a case report
<p>Abstract</p> <p>Introduction</p> <p>The application of lidocaine to the nasal mucosal area corresponding to the sphenopalatine fossa has been shown to be effective at extinguishing pain attacks in patients with a cluster headache. In this report, the effectiveness of local administration of lidocaine on cluster headache attacks as a symptomatic treatment of this disorder is discussed.</p> <p>Cases presentation</p> <p>A 22-year-old Turkish man presented with a five-year history of severe, repeated, unilateral periorbital pain and headache, diagnosed as a typical cluster headache. He suffered from rhinorrhea, lacrimation and ptosis during headaches. He had tried several unsuccessful daily medications. We applied a cotton tip with lidocaine hydrochloride into his left nostril for 10 minutes. The ptosis responded to the treatment and the intensity of his headache decreased.</p> <p>Conclusion</p> <p>Intranasal lidocaine is a useful treatment for the acute management of a cluster headache. Intranasal lidocaine blocks the neural transmission of the sphenopalatine ganglion, which contributes to the trigeminal nerve as well as containing both parasympathetic and sympathetic fibers.</p
Simultaneous Quantification and Identification of Individual Chemicals in Metabolite Mixtures by Two-Dimensional Extrapolated Time-Zero 1H−13C HSQC (HSQC0)
Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event Searches
The LUX-ZEPLIN (LZ) experiment will search for dark matter particle
interactions with a detector containing a total of 10 tonnes of liquid xenon
within a double-vessel cryostat. The large mass and proximity of the cryostat
to the active detector volume demand the use of material with extremely low
intrinsic radioactivity. We report on the radioassay campaign conducted to
identify suitable metals, the determination of factors limiting radiopure
production, and the selection of titanium for construction of the LZ cryostat
and other detector components. This titanium has been measured with activities
of U~1.6~mBq/kg, U~0.09~mBq/kg,
Th~~mBq/kg, Th~~mBq/kg, K~0.54~mBq/kg, and Co~0.02~mBq/kg (68\% CL).
Such low intrinsic activities, which are some of the lowest ever reported for
titanium, enable its use for future dark matter and other rare event searches.
Monte Carlo simulations have been performed to assess the expected background
contribution from the LZ cryostat with this radioactivity. In 1,000 days of
WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute
only a mean background of (stat)(sys) counts.Comment: 13 pages, 3 figures, accepted for publication in Astroparticle
Physic
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