2,304 research outputs found
A comparison of bone bed preparation with laser and conventional drill on the relationship between implant stability quotient (ISQ) values and implant insertion variables
X-ray observations of three young, early-type galaxies
Massive haloes of hot plasma exist around some, but not all elliptical galaxies. There is evidence that this is related to the age of the galaxy. In this paper, new X-ray observations are presented for three early-type galaxies that show evidence of youth, in order to investigate their X-ray components and properties. NGC 5363 and NGC 2865 were found to have X-ray emission dominated by purely discrete stellar sources. Limits are set on the mass distribution in one of the galaxies observed with XMM–Newton, NGC 4382, which contains significant hot gas. We detect the X-ray emission in NGC 4382 out to 4re. The mass-to-light ratio is consistent with a stellar origin in the inner regions but rises steadily to values indicative of some dark matter by 4re. These results are set in context with other data drawn from the literature, for galaxies with ages estimated from dynamical or spectroscopic indicators. Ages obtained from optical spectroscopy represent central luminosity-weighted stellar ages. We examine the X-ray evolution with age, normalized by B- and K-band luminosities. Low values of Log(LX/LB) and Log(LX/LK) are found for all galaxies with ages between 1 and 4 Gyr. Luminous X-ray emission only appears in older galaxies. This suggests that the interstellar medium is removed and then it takes several gigayears for hot gas haloes to build up, following a merger. A possible mechanism for gas expulsion might be associated with feedback from an active nucleus triggered during a merger
Enhanced heterogeneity of rpoB in Mycobacterium tuberculosis found at low pH.
OBJECTIVES: The aim of this study was to gain an insight into the molecular mechanisms of the evolution of rifampicin resistance in response to controlled changes in the environment. METHODS: We determined the proportion of rpoB mutants in the chemostat culture and characterized the sequence of mutations found in the rifampicin resistance-determining region of rpoB in a steady-state chemostat at pH 7.0 and 6.2. RESULTS: The overall proportion of rpoB mutants of strain H37Rv remained constant for 37 days at pH 7.0, ranging between 3.6 x 10(-8) and 8.9 x 10(-8); however, the spectrum of mutations varied. The most commonly detected mutation, serine to leucine mutation at codon 531 (S531L), increased from 40% to 89%, while other mutations (S531W, H526Y, H526D, H526R, S522L and D516V) decreased over the 37 day sampling period. Changing the pH from 7.0 to 6.2 did not significantly alter the overall proportion of mutants, but resulted in a decrease in the percentage of strains harbouring S531L (from 89% to 50%) accompanied by an increase in the range of different mutations from 4 to 12. CONCLUSIONS: The data confirm that the fitness of strains with the S531L mutation is greater than that of strains containing other mutations. We also conclude that at low pH the environment is permissive for a wider spectrum of mutations, which may provide opportunities for a successful mutant to survive
SHOCK ATTENUATION MECHANISM AT THE BACKPACK WEIGHT CHANGE IN DROP LANDINGS
The purpose of this study was to investigate the shock attenuation mechanisms while varying the loads in a backpack during drop landing. Ten subjects (age: 22.8±3.6, height: 173.5±4.3, weight: 70.4±5.2) performed drop landing under five varying loads (0, 5kg, 10kg, 20kg, 30kg). By employing two cameras (Sony VX2100) the following kinematic variables (phase time, joint rotational angle and velocity of ankle, knee and hip) were calculated by applying 2D motion analysis. Additional data, i.e. max vertical ground force (VGRF) and acceleration, was acquired by using two AMTI Force plates and a Noraxon Inline Accelerometer Sensor. Through analysing the power spectrum density (PSD), drop landing patterns were classified into four groups and each group was discovered to have a different shock attenuation mechanism. The first pattern that appeared at landing was that the right leg absorbed most of the shock attenuation. The second pattern to appear was that subject quickly transferred the load from the right leg to the left leg as quickly as possible. Thus, this illustrated that two shock attenuation mechanisms occurred during drop landing under varying load conditions
Technical and Economic Readiness Review of CFD-Based Numerical Wave Basin for Offshore Floater Design
Scalable scheme for entangling multiple ququarts using linear optical elements
We report a scalable linear optical scheme for generating entangled states of
multiple ququarts in which the individual single-ququart state is prepared with
the biphoton polarization state of frequency-nondegenerate spontaneous
parametric down-conversion. The output state is calculated with the full
consideration of the higher order effect (double-pair events) of spontaneous
parametric down-conversion. Scalability to multiple-ququart entanglement is
demonstrated with examples: linear optical entanglement of three and four
individual biphoton ququarts
Comparison of Hybrid RANS-LES Simulations of Turbulent Flow and Heat Transfer in a Ribbed Duct
A deep Chandra observation of the poor cluster AWM 4 - I. Properties of the central radio galaxy and its effects on the intracluster medium
Using observations from the Chandra X-ray Observatory and Giant Metrewave
Radio Telescope, we examine the interaction between the intracluster medium and
central radio source in the poor cluster AWM 4. In the Chandra observation a
small cool core or galactic corona is resolved coincident with the radio core.
This corona is capable of fuelling the active nucleus, but must be
inefficiently heated by jet interactions or conduction, possibly precluding a
feedback relationship between the radio source and cluster. A lack of clearly
detected X-ray cavities suggests that the radio lobes are only partially filled
by relativistic plasma. We estimate a filling factor of phi=0.21 (3 sigma upper
limit phi<0.42) for the better constrained east lobe. We consider the particle
population in the jets and lobes, and find that the standard equipartition
assumptions predict pressures and ages which agree poorly with X-ray estimates.
Including an electron population extending to low Lorentz factors either
reduces (gamma_min=100) or removes (gamma_min=10) the pressure imbalance
between the lobes and their environment. Pressure balance can also be achieved
by entrainment of thermal gas, probably in the first few kiloparsecs of the
radio jets. We estimate the mechanical power output of the radio galaxy, and
find it to be marginally capable of balancing radiative cooling.Comment: Accepted for publication in MNRAS, 18 pages, 9 postscript figures
Disturbed Fossil Group Galaxy NGC 1132
We have analyzed the Chandra archival data of NGC 1132, a well-known fossil
group, i.e. a system expected to be old and relaxed long after the giant
elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas
morphology is disturbed and asymmetrical, with a cold front following a
possible bow shock. We discuss possible origins of the disturbed hot halo,
including sloshing by a nearby object, merger, ram pressure by external hotter
gas and nuclear outburst. We consider that the first two mechanisms are likely
explanations for the disturbed hot halo, with a slight preference for a minor
merger with a low impact parameter because of the match with simulations and
previous optical observations. In this case, NGC 1132 may be a rare example of
unusual late mergers seen in recent simulations. Regardless of the origin of
the disturbed hot halo, the paradigm of the fossil system needs to be
reconsidered.Comment: 16 pages, 6 figures, accepted for publication in Ap
- …