679 research outputs found
A portable 28-GHz channel sounder platform and measurement results from close-to-ground field tests
This article describes a novel, bespoke, and low-cost 28-GHz RF TX and RX front end design that has been combined with a commercial Software-Defined Radio and Raspberry Pi controller to realize a portable propagation measurement system for the 28-GHz band. The complete sounder system can resolve an impulse from RX powers down to â107 dBm (3-dB impulse SNR) and the sounder TX can generate a signal of â8 dBm. Therefore, using 20-dBi antennas supports path-loss (PL) measurements of 139 dB. The sounder can resolve time-domain reflections to 33 ns in a channel measurement bandwidth of 60 MHz, producing both time-domain and frequency-domain results. The complete sounding system has been used to perform close-to-ground RF channel measurements, with propagation loss models and time-domain impulses extracted. Close-to-ground measurement is an underreported area of propagation research that is relevant for novel use-cases, such as in military applications or for mobile device-to-device communications. A key initial finding from the trials is that the PLs for 28-GHz indoor and outdoor links at circa 70 cm above ground seem close to that of free space, with very few strong reflections with delays exceeding 33 ns
Receive mode time modulated antenna array incorporating subsampling -theoretical concept and laboratory investigation
An eight element Subsampling Time Modulated Array (STMA) operating in receive mode with a carrier at 2.4 GHz is presented and demonstrated using bespoke Radio Frequency (RF) hardware. Each STMA cell incorporates subsampling functionality, with the sampling frequency significantly below the carrier frequency and requiring minimal additional hardware. By using this concept, the hardware required for a receiver incorporating an antenna array can be reduced and costs saved. STMA design equations and architecture strategies are presented, and a prototype hardware demonstrator is introduced. Laboratory measurements confirm that a received radiated signal, arranged to use the fundamental or a harmonic beam pointed at the radiating source, can be resolved from the subsampled intermediate frequency (IF) output. The concept demonstration hardware provides a measured array conversion gain of 11.4 dBi on the boresight beam, 7.8 dBi on the first positive and 11.3 dBi on the first negative harmonic beams, as resolved at the final combined IF output. The array IF output Signal to Noise and Distortion ratio is 69 dB. The dependence of array sidelobe level performance on STMA sampling switch rise time is also uncovered, though good performance with real, imperfect, hardware is still obtained
Transition Form Factor up to within the Factorization Approach
In the paper, we apply the factorization approach to deal with the
transition form factor in the large recoil
regions. The B-meson wave functions and that include the
three-particle Fock states' contributions are adopted to give a consistent PQCD
analysis of the form factor up to . It has been found that
both the wave functions and can give sizable
contributions to the form factor and should be kept for a better understanding
of the meson decays. Then the contributions from different twist structures
of the kaon wavefunction are discussed, including the -breaking
effects. A sizable contribution from the twist-3 wave function is
found, whose model dependence is discussed by taking two group of parameters
that are determined by different distribution amplitude moments obtained in the
literature. It is also shown that and
, which are more
reasonable and consistent with the light-cone sum rule results in the large
recoil regions.Comment: 22 pages and 6 figure
Parallelisation and application of AD3 as a method for solving large scale combinatorial auctions
Auctions, and combinatorial auctions (CAs), have been successfully employed to solve coordination problems in a wide range of application domains. However, the scale of CAs that can be optimally solved is small because of the complexity of the winner determination problem (WDP), namely of finding the bids that maximise the auctioneerâs revenue. A way of approximating the solution of a WDP is to solve its linear programming relaxation. The recently proposed Alternate Direction Dual Decomposition algorithm (AD3) has been shown to ef- ficiently solve large-scale LP relaxations. Hence, in this paper we show how to encode the WDP so that it can be approximated by means of AD3. Moreover, we present PAR-AD3, the first parallel implementation of AD3. PAR-AD3 shows to be up to 12.4 times faster than CPLEX in a single-thread execution, and up to 23 times faster than parallel CPLEX in an 8-core architecture. Therefore PAR- AD3 becomes the algorithm of choice to solve large-scale WDP LP relaxations for hard instances. Furthermore, PAR-AD3 has potential when considering large- scale coordination problems that must be solved as optimisation problems.Research supported by MICINN projects TIN2011-28689-C02-01, TIN2013-45732-C4-4-P and TIN2012-38876-C02-01Peer reviewe
The Spin Structure of the Proton and Polarized Collider Physics
We summarise the present status of the proton spin problem and the physics
possibilities for future polarized ep and pp colliders. This summary is based
on the presentations and discussion sessions at the workshop ``The Spin
Structure of the Proton and Polarized Collider Physics'' (Trento, July 23-28,
2001).Comment: 27 pages, 22 figure
Deeply virtual electroproduction of photons and mesons on the nucleon : leading order amplitudes and power corrections
We estimate the leading order amplitudes for exclusive photon and meson
electroproduction reactions at large Q^2 in the valence region in terms of
skewed quark distributions. As experimental investigations can currently only
be envisaged at moderate values of Q^2, we estimate power corrections due to
the intrinsic transverse momentum of the partons in the meson wavefunction and
in the nucleon. To this aim the skewed parton distribution formalism is
generalized so as to include the parton intrinsic transverse momentum
dependence. Furthermore, for the meson electroproduction reactions, we
calculate the soft overlap type contributions and compare with the leading
order amplitudes. We give first estimates for these different power corrections
in kinematics which are relevant for experiments in the near future.Comment: 59 pages, 21 figure
Evidence for two-quark content of in exclusive decays
Inspired by a large decay branching ratio (BR) of
measured by Belle recently, we propose that a significant evidence of the
component of in could be
demonstrated in exclusive decays by the observation of in
the final states and . We predict the BRs of to be () while
the unknown wave functions of () are chosen to fit the
observed decays of .Comment: 4 pages, 2 figures, Revtex4, version to appear in PR
Definition and Calculation of Bottom Quark Cross-Sections in Deep-inelastic Scattering at HERA and Determination of their Uncertainties
The uncertainties involved in the calculation of bottom quark cross-sections
in deep-inelastic scattering at HERA are studied in different phase space
regions. Besides the inclusive bottom quark cross-section, definitions closer
to the detector acceptance requiring at least one high energetic muon from the
semi-leptonic \bquark decay or a jet with high transverse energy are
investigated. For each case the uncertainties due to the choice of the
renormalisation and factorisation scale as well as the \bquark mass are
estimated in the perturbative NLO QCD calculation and furthermore uncertainties
in the fragmenation of the bottom quark to a B-meson and in its semi-leptonic
decay are discussed
Conformal mapping methods for interfacial dynamics
The article provides a pedagogical review aimed at graduate students in
materials science, physics, and applied mathematics, focusing on recent
developments in the subject. Following a brief summary of concepts from complex
analysis, the article begins with an overview of continuous conformal-map
dynamics. This includes problems of interfacial motion driven by harmonic
fields (such as viscous fingering and void electromigration), bi-harmonic
fields (such as viscous sintering and elastic pore evolution), and
non-harmonic, conformally invariant fields (such as growth by
advection-diffusion and electro-deposition). The second part of the article is
devoted to iterated conformal maps for analogous problems in stochastic
interfacial dynamics (such as diffusion-limited aggregation, dielectric
breakdown, brittle fracture, and advection-diffusion-limited aggregation). The
third part notes that all of these models can be extended to curved surfaces by
an auxilliary conformal mapping from the complex plane, such as stereographic
projection to a sphere. The article concludes with an outlook for further
research.Comment: 37 pages, 12 (mostly color) figure
Hadronic final states in deep-inelastic scattering with Sherpa
We extend the multi-purpose Monte-Carlo event generator Sherpa to include
processes in deeply inelastic lepton-nucleon scattering. Hadronic final states
in this kinematical setting are characterised by the presence of multiple
kinematical scales, which were up to now accounted for only by specific
resummations in individual kinematical regions. Using an extension of the
recently introduced method for merging truncated parton showers with
higher-order tree-level matrix elements, it is possible to obtain predictions
which are reliable in all kinematical limits. Different hadronic final states,
defined by jets or individual hadrons, in deep-inelastic scattering are
analysed and the corresponding results are compared to HERA data. The various
sources of theoretical uncertainties of the approach are discussed and
quantified. The extension to deeply inelastic processes provides the
opportunity to validate the merging of matrix elements and parton showers in
multi-scale kinematics inaccessible in other collider environments. It also
allows to use HERA data on hadronic final states in the tuning of hadronisation
models.Comment: 32 pages, 22 figure
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