1,348 research outputs found
The Roles of âConventionalâ and Demand-Responsive Bus Services
Purpose - The roles of âconventionalâ (fixed-route and fixed-timetable) bus services is examined and compared to demand-responsive services, taking rural areas in England as the basis for comparison. It adopts a âruralâ definition of settlements under a population of 10,000.
Design/methodology/approach - Evidence from the National Travel Survey, technical press reports and academic work is brought together to examine the overall picture.
Findings - Inter-urban services between towns can provide a cost-effective way of serving rural areas where smaller settlements are suitably located. The cost structures of both fixed-route and demand-responsive services indicate that staff time and cost associated with vehicle provision are the main elements. Demand-responsive services may enable larger areas to be covered, to meet planning objectives of ensuring a minimum of level of service, but experience often shows high unit cost and public expenditure per passenger trip. Economic evaluation indicates user benefits per passenger trip of similar magnitude to existing average public expenditure per trip on fixed-route services. Considerable scope exists for improvements to conventional services through better marketing and service reliability.
Practical implications - The main issue in England is the level of funding for rural services in general, and the importance attached to serving those without access to cars in such areas.
Social implications - The boundary between fixed-route and demand-responsive operation may lie at relatively low population densities.
Originality/value - The chapter uses statistical data, academic research and operator experience of enhanced conventional bus services to provide a synthesis of outcomes in rural areas
Cooling of high-power-density computer components
This report summarizes work carried out during the first two years of a research program sponsored by IBM Corporation. This study has elucidated a number of the heat-transfer characteristics of several fluorochemicals which have potential application as coolants for high power density computer components. Single-phase heat-transfer coefficients have been determined for Freon-113 and FC-78 flowing in a rectangular channel with one of the wide sides heated. Heat-transfer coefficients for the short channels are significantly higher than those predicted by conventional correlations due to entrance effects and superimposed free convection. Uncertainties as to the actual values of certain thermophysical properties introduce corresponding uncertainty in correlation. Subcooled flow boiling data were taken with the rectangular channel for a wide variety of fluid-surface combinations, and over a wide range of flow conditions. These data should facilitate a close estimate of surface temperatures in actual systems. Data taken with an annular test section delineated hysteresis effects which were tentatively identified in the rectangular channel tests. Pool boiling tests indicated large temperature overshoots in the boiling curve with Freon-113. It was found that conventional correlations do not adequately describe critical heat flux data for horizontal circular heaters. The critical heat flux increases as diameter decreases, and increases as the wall thickness increases. The observed hysteresis effects in pool and flow boiling were examined in detail. It is suggested that the phenomenon of temperature overshoot hysteresis is due to two causes: a) the existence of metastable bubbles which are triggered only at sufficiently high disturbance level, and b) the deactivation of larger nucleation sites by displacing the vapor by liquid during subcooling.(cont.) Under conditions of low velocity or pool boiling, a) is probably most important, but at high velocity b) should be controlling. Increased heat-transfer coefficients observed prior to nucleation appear to be due to thermocapillary circulation induced by the metastable bubbles. It is demonstrated that a random array of Teflon pits on the surface is effective in augmenting heat transfer for pool boiling or low velocity flow boiling of water; however, there is no improvement in heat transfer with boiling of Freon-113 or FC-78. The mechanism of augmentation is examined from the standpoint of incipient boiling, and a plausible explanation for this behavior is suggested. An investigation of the factors controlling the void fraction for subcooled boiling was carried out with a horizontal visual section using Freon-113 and Freon TA. The observed point of net vapor generation was much farther upstream than that indicated by a recent prediction, due primarily to the dominance of the buoyant force. An examination of the void collapse in the unheated downstream portion of the tube revealed that bubble collapse theory cannot be used to predict the void fraction. The large void fractions produced by boiling fluorochemicals can be minimized by using twisted-tape inserts.Heat Transfer Development Laboratory, Systems Development Division, International Business Machines Corporation Massachusetts Institute of Technology, Division of Sponsored Researc
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ âJ/ÏK
+, B0 âJ/ÏK
â0 and B0 âD
ââ
Ό
+
ΜΌ decay
modes with 0.37 fbâ1 of data collected in pp collisions
at
â
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ â J/ÏK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Measurement of the relative rate of prompt Ïc0, Ïc1 and Ïc2 production at âs=7TeV
Prompt production of charmonium Ïc0, Ïc1 and Ïc2 mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of âs=7TeV. The Ïc mesons are identified through their decay to J/ÏÎł, with J/ÏâÎŒ+muâ using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of 1.0fbâ1 collected by the LHCb detector, is used to measure the relative prompt production rate of Ïc1 and Ïc2 in the rapidity range 2.0<y<4.5 as a function of the J/Ï transverse momentum from 3 to 20 GeV/c. First evidence for Ïc0 meson production at a hadron collider is also presented
Measurement of the lifetime
Using a data set corresponding to an integrated luminosity of ,
collected by the LHCb experiment in collisions at centre-of-mass energies
of 7 and 8 TeV, the effective lifetime in the
decay mode, , is measured to be ps. Assuming
conservation, corresponds to the lifetime of the light
mass eigenstate. This is the first measurement of the effective
lifetime in this decay mode.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-017.htm
Observation of excited Lambda_b0 baryons
Using pp collision data corresponding to 1.0 fb-1 integrated luminosity
collected by the LHCb detector, two narrow states are observed in the
Lambda_b0pi+pi- spectrum with masses 5911.97 +- 0.12(stat) +- 0.02(syst) +-
0.66(Lambda_b0 mass) MeV/c^2 and 5919.77 +- 0.08(stat) +- 0.02(syst) +-
0.66(Lambda_b0 mass) MeV/c^2. The significances of the observations are 5.2 and
10.2 standard deviations, respectively. These states are interpreted as the
orbitally-excited Lambda_b0 baryons, Lambda_b*0(5912) and Lambda_b*0(5920).Comment: Replaced by version published in Phys. Rev. Lett, modified fit with
better mass resolution treatmen
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