2,266 research outputs found
Achieving satisfactory contractual terms for the engineer's role
An international survey of clients, consultants and contractors produced wide-ranging data on the views of users of the FIDIC form of contract. The purpose of the survey was to elicit views on a range of issues, prior to revising the model form, to ensure that the contract drafters produce a form that is satisfactory for its users. Those questions that focus upon the role of the engineer have been subjected to detailed statistical analysis. The analysis shows that, contrary to popular belief, the views of contract users from common law jurisdictions do not differ from those in civil code jurisdictions. The engineerâs role is not generally perceived as neutral in the contractual relationships between clients and contractors. Contractors would prefer someone other than the engineer to be the first-line settler of disputes in contracts
Surface MIMO: Using Conductive Surfaces For MIMO Between Small Devices
As connected devices continue to decrease in size, we explore the idea of
leveraging everyday surfaces such as tabletops and walls to augment the
wireless capabilities of devices. Specifically, we introduce Surface MIMO, a
technique that enables MIMO communication between small devices via surfaces
coated with conductive paint or covered with conductive cloth. These surfaces
act as an additional spatial path that enables MIMO capabilities without
increasing the physical size of the devices themselves. We provide an extensive
characterization of these surfaces that reveal their effect on the propagation
of EM waves. Our evaluation shows that we can enable additional spatial streams
using the conductive surface and achieve average throughput gains of 2.6-3x for
small devices. Finally, we also leverage the wideband characteristics of these
conductive surfaces to demonstrate the first Gbps surface communication system
that can directly transfer bits through the surface at up to 1.3 Gbps.Comment: MobiCom '1
Differential effects of anti-CD20 therapy on CD4 and CD8 T cells and implication of CD20-expressing CD8 T cells in MS disease activity
A small proportion of multiple sclerosis (MS) patients develop new disease activity soon after starting anti-CD20 therapy. This activity does not recur with further dosing, possibly reflecting deeper depletion of CD20-expressing cells with repeat infusions. We assessed cellular immune profiles and their association with transient disease activity following anti-CD20 initiation as a window into relapsing disease biology. Peripheral blood mononuclear cells from independent discovery and validation cohorts of MS patients initiating ocrelizumab were assessed for phenotypic and functional profiles using multiparametric flow cytometry. Pretreatment CD20-expressing T cells, especially CD2
Similarity In Phase Diagrams Between Ionic And Nonionic Surfactant Solutions At Constant Temperature
Irreducible characters of GSp(4, q) and dimensions of spaces of fixed vectors
In this paper, we compute the conjugacy classes and the list of irreducible
characters of GSp(4,q), where q is odd. We also determine precisely which
irreducible characters are non-cuspidal and which are generic. These characters
are then used to compute dimensions of certain subspaces of fixed vectors of
smooth admissible non-supercuspidal representations of GSp(4,F), where F is a
non-archimedean local field of characteristic zero with residue field of order
q.Comment: 48 pages, 21 tables. Corrected an error in Table 16 for type V*
representations (theta_11 and theta_12 were switched
Recent X-ray measurements of the accretion-powered pulsar 4U 1907+09
X-ray observations of the accreting X-ray pulsar 4U~1907+09, obtained during
February 1996 with the Proportional Counter Array on the Rossi X-ray Timing
Experiment (RXTE), have enabled the first measurement of the intrinsic pulse
period Ppulse since 1984: Ppulse=440.341[+0.012,-0.017] s. 4U 1907+09 is in a
binary system with a blue supergiant. The orbital parameters were solved and
this enabled the correction for orbital delay effects of a measurement of
Ppulse obtained in 1990 with Ginga. Thus, three spin down rates could be
extracted from four pulse periods obtained in 1983, 1984, 1990, and 1996. These
are within 8% equal to a value of dPpulse/dt=+0.225 s/yr. This suggest that the
pulsar is perhaps in a monotonous spin down mode since its discovery in 1983.
Furthermore, the RXTE observations show transient ~18 s oscillations during a
flare that lasted about 1 hour. The oscillations may be interpreted as
Keplerian motion of an accretion disk near the magnetospheric radius. This, and
the notion that the co-rotation radius is much larger than any conceivable
value for the magnetospheric radius (because of the long spin period), renders
it unlikely that this pulsar spins near equilibrium like is suspected for other
slowing accreting X-ray pulsars. We suggest as an alternative that perhaps the
frequent occurrence of a retrograde transient accretion disk may be
consistently slowing the pulsar down. Further observations of flares can
provide more evidence of this.Comment: 26 pages, 11 figures, to be published in Astrophysical Journal part I
on March 20, 199
Sonic-Point Model of Kilohertz Quasi-Periodic Brightness Oscillations in Low-Mass X-ray Binaries
Strong, coherent, quasi-periodic brightness oscillations (QPOs) with
frequencies ranging from about 300 Hz to 1200 Hz have been discovered with the
Rossi X-ray Timing Explorer in the X-ray emission from some fifteen neutron
stars in low-mass binary systems. Two simultaneous kilohertz QPOs differing in
frequency by 250 to 350 Hertz have been detected in twelve of the fifteen
sources. Here we propose a model for these QPOs. In this model the X-ray source
is a neutron star with a surface magnetic field of 10^7 to 10^10 G and a spin
frequency of a few hundred Hertz, accreting gas via a Keplerian disk. The
frequency of the higher-frequency QPO in a kilohertz QPO pair is the Keplerian
frequency at a radius near the sonic point at the inner edge of the Keplerian
flow whereas the frequency of the lower-frequency QPO is approximately the
difference between the Keplerian frequency at a radius near the sonic point and
the stellar spin frequency. This model explains naturally many properties of
the kilohertz QPOs, including their frequencies, amplitudes, and coherence. We
show that if the frequency of the higher-frequency QPO in a pair is an orbital
frequency, as in the sonic-point model, the frequencies of these QPOs place
interesting upper bounds on the masses and radii of the neutron stars in the
kilohertz QPO sources and provide new constraints on the equation of state of
matter at high densities. Further observations of these QPOs may provide
compelling evidence for the existence of a marginally stable orbit, confirming
a key prediction of general relativity in the strong-field regime.Comment: 67 pages, including 15 figures and 5 tables; uses aas2pp4; final
version to appear in the Astrophysical Journal on 1 December 199
Dose ratio proton radiography using the proximal side of the Bragg peak
Purpose: In recent years there has been a movement towards single-detector proton radiography, due to its potential ease of implementation within the clinical environment. One such single-detector technique is the dose ratio method, in which the dose maps from two pristine Bragg peaks are recorded beyond the patient. To date, this has only been investigated on the distal side of the lower energy Bragg peak, due to the sharp fall-off. We investigate the limits and applicability of the dose ratio method on the proximal side of the lower energy Bragg peak, which has the potential to allow a much wider range of water-equivalent thicknesses (WET) to be imaged. Comparisons are made with the use of the distal side of the Bragg peak. Methods: Using the analytical approximation for the Bragg peak we generated theoretical dose ratio curves for a range of energy pairs, and then determined how an uncertainty in the dose ratio would translate to a spread in the WET estimate. By defining this spread as the accuracy one could achieve in the WET estimate, we were able to generate look-up graphs of the range on the proximal side of the Bragg peak that one could reliably use. These were dependent on the energy pair, noise level in the dose ratio image and the required accuracy in the WET. Using these look-up graphs we investigated the applicability of the technique for a range of patient treatment sites. We validated the theoretical approach with experimental measurements using a complementary metal oxide semiconductor active pixel sensor (CMOS APS), by imaging a small sapphire sphere in a high energy proton beam. Results: Provided the noise level in the dose ratio image was 1% or less, a larger spread of WETs could be imaged using the proximal side of the Bragg peak (max 5.31 cm) compared to the distal side (max 2.42 cm). In simulation it was found that, for a pediatric brain, it is possible to use the technique to image a region with a square field equivalent size of 7.6 cm2, for a required accuracy in the WET of 3 mm and a 1% noise level in the dose ratio image. The technique showed limited applicability for other patient sites. The CMOS APS demonstrated a good accuracy, with a root-mean-square-error of 1.6 mm WET. The noise in the measured images was found to be Ï =1.2% (standard deviation) and theoretical predictions with a 1.96Ï noise level showed good agreement with the measured errors. Conclusions: After validating the theoretical approach with measurements, we have shown that the use of the proximal side of the Bragg peak when performing dose ratio imaging is feasible, and allows for a wider dynamic range than when using the distal side. The dynamic range available increases as the demand on the accuracy of the WET decreases. The technique can only be applied to clinical sites with small maximum WETs such as for pediatric brains
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