2,125 research outputs found
Stress redistribution due to creep in nimonic 90 ministry of aviation contract no. PD/28/021 report for the period June, 1965 to July, 1966: part 2
Part I of this report, dated September 1965, deals mainly with
the design and construction of the special apparatus to simulate the
stress redistribution occurring during the creep of a cooled turbine
blade. It reported some preliminary experiments using aluminium alloy
test specimens.
During the past year, the period covered by this report, a series
of experiments have been completed using specimens machined from nimonic
90 alloy.
Experience gained in operating the apparatus, have resulted in
several modifications both to the apparatus and the associated instrumentation.
These are detailed within this report
Stress redistribution due to creep in nimonic 90 ministry of aviation contract no. PD/28/021 report for the period January 1964 - June 1965: part 1
The period covered by this report has been devoted to the design,
construction development and calibration of a special apparatus to simulate
the stress redistribution conditions occurring during the creep of a cooled
turbine blade. The experimental assembly consists of two creep machines,
each operating at a different temperature, so controlled that a load is
shared between them. maintaining equal creep strains (and in consequence
equal creep rates) in each specimen. The stress in each specimen and the
creep strain of the pair are automatically measured and recorded by a
specially developed unit. Some preliminary results on an aluminium alloy
are presented
The development and evaluation of an ultrasonic fatigue unit
A fatigue test apparatus operating at 20 kc/s is described. The unit is based
on a standard magnetostrictive drive system as used in high energy stresswave
generators. An automatic counting device has been developed and incorporated
in the final equipment, resulting in improvements in accuracy and reproducibility
of results. Some typical results of tests on aluminium alloys are presented
The Method of Images in Cosmology
31 pages, 18 figures31 pages, 18 figuresWe apply the method of images to the exact initial data for cosmological models that contain a number of regularly arranged discrete masses. This allows us to join cosmological regions together by throats, and to construct wormholes in the initial data. These wormholes allow for the removal of the asymptotically flat "flange" regions that would otherwise exist on the far side of black holes. The method of images also provides us with a way to investigate the definition of mass is cosmology, and the cosmological consequences of the gravitational interaction energies between massive objects. We find evidence that the interaction energies within clusters of massive objects do indeed appear to contribute to the total energy budget in the cosmological regions of the space-time
Cosmological solutions with charged black holes
RB aknowledges support from the Higher Education Commission (HEC) of Pakistan, which provided funding to visit QMUL while this work was performed. TC and JD are supported by the STFC
The design and construction of a weld heat-affected zone simulator
Investigation of the structure and properties of the heat-affected zones
in welded joints is usually limited by their small size and their complexity.
One method of overcoming this problem is to simulate the structure at a
particular point in the heat-affected zone in a specimen of larger size by
imposing on it the thermal cycle sustained at that point.
The equipment described in this note uses a.c. resistance heating and
water cooling to impose thermal cycles on 2.5" x O.W' x O.W' specimens, the
thermal cycle being chosen by adjustment of a bank of variable resistors to
construct a voltage analogue. Control of specimen temperature is achieved
using a thyristor and two ignitrons to control the input at 44ov. to a
welding transformer. Feedback is applied from a thermocouple welded to the
specimen hot-zone. The equipment has been shown to produce the desired
thermal cycles in a reproducible manner
Push-pull fatigue properties of wires in an iridium - 5% tungsten alloy
Introduction
This memorandum reports a series of tests to determine the fatigue
properties of an iridium - 5% tungsten alloy at 600°c and 700°C.
A previous memorandum, Memo. Mat. 61, reports the fatigue properties
at room temperature of the same alloy
A quasi-static approach to structure formation in black hole universes
JD and TC both acknowledge support from the STFC under grant STFC ST/N504257/1
Dynamics of a lattice Universe
We find a solution to Einstein field equations for a regular toroidal lattice
of size L with equal masses M at the centre of each cell; this solution is
exact at order M/L. Such a solution is convenient to study the dynamics of an
assembly of galaxy-like objects. We find that the solution is expanding (or
contracting) in exactly the same way as the solution of a
Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average
density as our model. This points towards the absence of backreaction in a
Universe filled with an infinite number of objects, and this validates the
fluid approximation, as far as dynamics is concerned, and at the level of
approximation considered in this work.Comment: 14 pages. No figure. Accepted version for Classical and Quantum
Gravit
Chandra Observation of PSR B1823-13 and its Pulsar Wind Nebula
We report on an observation of the Vela-like pulsar B1823-13 and its
synchrotron nebula with Chandra.The pulsar's spectrum fits a power-law model
with a photon index Gamma_PSR=2.4 for the plausible hydrogen column density
n_H=10^{22} cm^{-2}, corresponding to the luminosity L_PSR=8*10^{31} ergs
s^{-1} in the 0.5-8 keV band, at a distance of 4 kpc. The pulsar radiation
likely includes magnetospheric and thermal components, but they cannot be
reliably separated because of the small number of counts detected and strong
interstellar absorption. The pulsar is surrounded by a compact, 25''x 10'',
pulsar wind nebula (PWN) elongated in the east-west direction, which includes a
brighter inner component, 7''x 3'', elongated in the northeast-southwest
direction. The slope of the compact PWN spectrum is Gamma_comp=1.3, and the
0.5-8 keV luminosity is L_comp~3*10^{32} ergs s^{-1}. The compact PWN is
surrounded by asymmetric diffuse emission (extended PWN) seen up to at least
2.4' south of the pulsar, with a softer spectrum (Gamma_ext=1.9), and the 0.5-8
keV luminosity L_ext~10^{33}-10^{34} ergs s^{-1}. We also measured the pulsar's
proper motion using archival VLA data: \mu_\alpha=23.0+/-2.5 mas yr^{-1},
\mu_\delta=-3.9+/-3.3 mas yr^{-1}, which corresponds to the transverse
velocity v_perp=440 km s^{-1}. The direction of the proper motion is
approximately parallel to the elongation of the compact PWN, but it is nearly
perpendicular to that of the extended PWN and to the direction towards the
center of the bright VHE gamma-ray source HESS J1825-137, which is likely
powered by PSR B1823-13.Comment: 13 pages, 8 figures and 3 tables; submitted to Ap
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