1,820 research outputs found
ATMOSPHERIC EMISSION MODELS - CONFRONTATION BETWEEN OBSERVATIONAL DATA AND PREDICTIONS IN THE 2.5-300 GHZ FREQUENCY-RANGE
No full textFeshbach spectroscopy of an ultracold Rb-Cs mixture
No full textThis thesis reports the observation of interspecies Feshbach resonances in an ultracold mixture of Rb and Cs atoms. A versatile combined magnetic and optical potential has been designed and constructed which is capable of bringing both and to degeneracy, and reaching high phase-space density in . High phase-space density mixtures are the first step required in the production of ultracold polar molecules, the topic of much current research.
The apparatus capitalises on the efficient capture of atoms by a magnetic trap from a magneto-optical trap, and the efficient sympathetic cooling of Cs by Rb therein. Upon transfer to the crossed optical dipole trap condensates in excess of atoms and approximately atoms are produced after direct evaporation and gravito-magnetic tilting of the potential. The observation of six interspecies - Feshbach resonances are reported, three of which had only been predicted theoretically, allowing testing and development of the theoretical model. Furthermore, the extrapolation of this model has predicted numerous Feshbach resonances between and , none of which have been experimentally observed prior to this work. The versatile nature of this apparatus is discussed, including the application of the current system to cooling of . Initial experiments observed seven interspecies resonances, including a broad s-wave resonance at a magnetic field of G which is in excellent agreement with the theoretical prediction. Further work has revealed that fourteen Feshbach resonances exist in the 0-700 G magnetic field range between and atoms in the and states, respectively. Several of these resonances would be ideal for magneto-association of RbCs molecules, prior to transfer to the rovibrational ground-state
Can epigenetic changes in DNA methylations explain the altered gene expression in osteoarthritis?
No full textClonal chondrocytes of osteoarthritic (OA) cartilage express an aberrant set of genes. We hypothesize that this aberrant gene expression may be due to clonally inherited epigenetic changes, defined as altered gene expression without changes in genetic sequence. The major epigenetic changes are due to altered DNA methylations in crucial parts of the promoter region. If the cytosines of CpG dinucleotides are methylated, the gene will be silenced, even if the right transcription factors are present. Similarly, de-methylations may activate previously silenced genes. Our aims were to provide ‘proof-of-concept’ data by examining the methylation status of genes in OA vs non-OA chondrocytes. Articular cartilage was obtained a) from the cartilage of fracture-neck-of-femur (#NOF) patients and b) from or around the eroded regions of OA samples. The former was full thickness cartilage, the latter was partially degraded cartilage, which contained mostly clonal chondrocytes as confirmed by histology. The cartilage samples were ground in a freezer mill (Glen Creston, UK) and DNA was extracted with a Qiagen DNeasy maxi kit. To assess DNA methylation status, the genomic DNA was treated overnight with methylation-sensitive restriction enzymes. Cleavage of selected sites was detected by PCR amplifications with primer pairs designed to bracket selected promoter regions. Loss of the PCR band after digestion with the enzymes indicated absence of methylations, whereas presence of the band indicated methylated cytosine. We selected MMP-9 as one of genes that is activated in OA. Transcription of mmp-9 is regulated by a 670 bp sequence at the 5'-end flanking region, which contains 6 CpGs and a further 21 CpGs within the 1.5 kb region further upstream. A PCR primer pair was designed to bracket a 350bp sequence upstream from the transcription start site of mmp-9, which contained four of the six potential methylation sites, cleaved by the methylation-sensitive enzymes AciI and HhaI. DNA from 9 OA patients, 5 #NOF patients and 1 rheumatoid arthritic (RA) patient were digested with HhaI or AciI and examined for the presence or absence of PCR bands. In all patients, digestion with HhaI abolished the PCR band, indicating that the HhaI site was never methylated in either #NOF or OA patients. However, a remarkable difference was found after digestion with AciI: in 8/9 OA patients, the PCR band was no longer detectable, while in 4/5 #NOF patients the PCR band was still present. This suggested that all three AciI cleavage sites were methylated in the majority of chondrocytes from #NOF patients, while at least one of the three AciI cleavage sites was unmethylated in OA patients. Interestingly, the PCR band was present in the RA patient, suggesting methylation of the AciI cleavage sites. The present study provides the first ‘proof-of-concept’ data that suggest epigenetic changes may play a role in the etiology of osteoarthritis. Clearly further work is required to establish the generality of the present findings and whether de-methylations are also found in the promoter regions of other genes that are aberrantly expressed in OA
A Quantum Degenerate Mixture of Rb and Cs
No full textThis thesis reports the formation of a dual-species Bose-Einstein condensate of Rb and Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation.
The experimental method exploits the efficient sympathetic cooling of Cs via elastic collisions with Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate \mbox{~cms}. The two condensates each contain up to \mbox{} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the Rb during the cooling leads to the creation of single-species Cs condensates of up to \mbox{} atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)~G and the creation of a pure sample of Cs molecules via magneto-association on the 4(g)4 resonance at 19.8~G. These results represent important steps towards the creation of ultracold polar RbCs molecules
Realisation of a cold mixture of rubidium and caesium
No full textThis thesis describes a new apparatus designed to study cold, ultracold, and quantum degenerate mixtures of rubidium and caesium atoms. The Rb- Cs mixture is prepared using a double magneto-optical trap (MOT) system in which a two-species pyramid MOT acts as a source of cold atoms for a 'science' MOT. The first results of experiments on the magneto-optically trapped mixture are presented, including measurements of trap loss rates due to single-species and interspecies inelastic collisions. A technique for reducing interspecies loss by spatially separating the MOTs during loading is described. This technique allows 50-50 mixtures of Rb and Cs atoms to be loaded into a magnetic trap at close to their respective maximum single- species atom numbers. Alternatively, one species can be loaded with arbitrarily small amounts of the other. The displaced MOT technique is thus аn excellent starting point for investigations of interspecies Feshbach resonances and sympathetic cooling of Rb-Cs mixtures in magnetic and optical traps. In addition, a model of polarisation spectroscopy based on numerical integration of population rate equations is described. Theoretical polarisation spectra generated by the model are shown to agree with experimental spectra for the F = I + 1/2 → F' transitions in Rb and Cs. An investigation of the sub-Doppler dichroic atomic vapour laser locking (DAVLL) technique demonstrates how locking signals can be optimised for the Rb D2 transitions. The role of polarisation purity in generating the spectra is discussed, and impurities are modeled using a Jones matrix approach. Comparisons with polarisation spectroscopy and DAVLL are used to enhance understanding of atom-light interactions in spectroscopic systems, and indicate methods for optimising locking signals for use in cold atom experiments
Nurse led versus lay educators support for those with asthma in primary care: a costing study
No full text<p>Background - Regular review and support for asthma self-management is promoted in guidelines. A randomised controlled trial suggested that unscheduled health care usage was similar when patients were offered self management support by a lay-trainer or practice nurses.</p>
<p>Methods - Following the RCT, a costing study was undertaken using the trial data to account for the cost of delivery of the service under both strategies and the resulting impact on unscheduled healthcare (measure of effectiveness) in this trial.</p>
<p>Results - One year data (n = 418) showed that 29% (61/205) of the nurse group required unscheduled healthcare (177 events) compared with 30.5% (65/213) for lay-trainers (178 events).</p>
<p>The training costs for the lay-trainers were greater than nurses (£36 versus £18 respectively per patient, p<0.001), however, the consultation cost for lay-trainers were lower than nurses (£6 per patient versus £24, p<0.001). If the cost of unscheduled healthcare are accounted for then the costs of nurses is £161, and £135 for lay-trainers (mean difference £25, [95% CI = −£97, £149, p = 0.681]). The total costs (delivery and unscheduled healthcare) were £202 per patient for nurses versus £178 for lay-trainers, (mean difference £24, [95%CI = −£100, £147, p = 0.707]).</p>
<p>Conclusions - There were no significant differences in the cost of training and healthcare delivery between nurse and lay trainers, and no significant difference in the cost of unscheduled health care use.</p>
Liquid structure of Rb-Hg alloys studied by neutron diffraction
No full textThe structures of liquid Rb–Hg alloys were studied as a function of composition by neutron diffraction. In the intermediate Rb concentration range, the obtained structure factors show a small prepeak, which may be an evidence of the formation of Hg polyanion units in liquids. The Reverse Monte Carlo (RMC) analysis was applied to separate the total radial distribution function into the corresponding partial radial distribution functions. Up to 10 at.% Rb, no obvious changes are found for the first peak position of the partial radial distribution functions of the Hg–Hg pair and that of the Hg–Rb pair. The first peak position between the Hg–Rb pairs increases above 20 at.% Rb. In addition to the first peak, a subpeak between Hg–Hg pairs can be seen in the large distance. At 60 at.% Rb, the nearest neighbor distance between Hg atoms shows the closest value in the concentration range studied. These results indicate that with the progress of charge transfer the solvation structure in the dilute Rb concentration range changes into the structure containing polyanions composed of Hg species
Observations of the diffuse near-IR sky emission with a balloon-borne infrared telescope (TRIP)
No full textThe diffuse sky emission in 7 spectral bands between 2 and 4.6 microns has been observed with a cooled balloon-borne IR telescope (TRIP). The results, reported here, confirm state-of-the-art atmospheric models for the continuum emission lambda > 3 mu m and for the OH component at lambda < 2.3 mu m. On the other hand, excess flux in the 2.3 to 2.5 mu m atmospheric window is found at a level of lambda I-lambda similar or equal to 1.5 - 2 10(-10) W cm(-2) sr(-1). Given its modulation with the zenith angle, this signal can be attributed to residual atmospheric emission, possibly due to narrow saturated absorption lines. The sky brightness detected by TRIP in the atmospheric window is 1.5 magnitude fainter at balloon altitudes than the typical sky brightness at South Pole. However, in optimal atmospheric conditions, the sky brightness at South Pole can be only half a magnitude brighter
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