An S-FSCW Based Multi-Channel Reader System for Beamforming Applications using Surface Acoustic Wave Sensors

Interrogating multiple surface acoustic wave (SAW) sensors located within the same radar beam require techniques to separate the multiple superposing SAW sensor responses. The presented multi-channel reader features four parallel transceiver channels, which are based on the switched frequency-stepped continuous-wave principle and high-speed parallelized baseband electronics. Thus classical beamforming applications including angle of arrival measurement of single SAW tags and the angular separation of multiple SAW sensors are presented and compared to a multiple-input multiple-output (MIMO) approach. Due to the larger virtual array in the MIMO approach a larger aperture can be synthesized, which leads to significantly better angular separation results. The level analysis for the given system is verified by baseband-power measurements at different readout distances, considering the hardware parameters as well as the free-space propagation aspects. Finally measurements assess the maximum interrogation distance for the system

The Expansion in Width for Domain Walls in Nematic Liquid Crystals in External Magnetic Field

The improved expansion in width is applied to curved domain walls in uniaxial nematic liquid crystals in external magnetic field. In the present paper we concentrate on the case of equal elastic constants. We obtain approximate form of the director field up to second order in magnetic coherence length.Comment: 18 pages, Latex 2.09, no figure

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5_aMC@NLO, capable of handling all these computations -- parton-level fixed order, shower-matched, merged -- in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV $e^+e^-$ collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.Comment: 158 pages, 27 figures; a few references have been adde

Top Quark Spin Polarization in ep Collision

We discuss the degree of spin polarization of single top quarks produced via $Wg$ fusion process in $ep$ collision at TESLA+HERAp and CLIC+LHC energies $\sqrt{s}=1.6$ and 5.3 TeV. For $eb \to t \bar{\nu}$ subprocess we show that the top quark spin is completely polarized when the spin basis is chosen in the direction of the incoming positron beam in the rest frame of top quark. A description on how to combine the cross sections of $e^{+}b\to t\bar{\nu}$ and $e^{+}g\to t\bar{b}\bar{\nu}$ processes is given. $e^{+}$-beam direction is taken to be the favorite top quark spin decomposition axis in its rest frame and it is found to be comparable with the ones in $pp$ collision. It is argued that theoretical simplicity and experimental clearness are the advantage of $ep$ collision.Comment: Revised version of Phys. Rev. D69 (2004)03401

Director configuration of planar solitons in nematic liquid crystals

The director configuration of disclination lines in nematic liquid crystals in the presence of an external magnetic field is evaluated. Our method is a combination of a polynomial expansion for the director and of further analytical approximations which are tested against a numerical shooting method. The results are particularly simple when the elastic constants are equal, but we discuss the general case of elastic anisotropy. The director field is continuous everywhere apart from a straight line segment whose length depends on the value of the magnetic field. This indicates the possibility of an elongated defect core for disclination lines in nematics due to an external magnetic field.Comment: 12 pages, Revtex, 8 postscript figure

Measuring effective electroweak couplings in single top production at the LHC

We study the mechanism of single top production at the LHC in the framework of an effective electroweak Lagrangian, analyzing the sensitivity of different observables to the magnitude of the effective couplings that parametrize new physics beyond the Standard Model. The observables relevant to the distinction between left and right effective couplings involve in practice the measurement of the spin of the top and this can be achieved only indirectly by measuring the angular distribution of its decay products. We show that the presence of effective right-handed couplings implies that the top is not in a pure spin state. A unique spin basis is singled out which allows one to connect top decay products angular distribution with the polarized top differential cross section. We present a complete analytical expression of the differential polarized cross section of the relevant perturbative subprocess including general effective couplings. The mass of the bottom quark, which actually turns out to be more relevant than naively expected, is retained. Finally we analyze different aspects the total cross section relevant to the measurement of new physics through the effective couplings. The above analysis also applies to anti-top production in a straightforward way.Comment: 38 pages, 17 figure

TYC 8380-1953-1: Discovery of an RS CVn binary through the XMM-Newton slew survey

In this paper we report the discovery of the chromospherically active (RS CVn type) binary TYC 8380-1953-1 through the XMM-Newton slew survey and present results of our optical and X-ray follow-up. With a flux limit of $6 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the soft band ($0.2 - 2$ keV), the XMM-Newton slew has a similar sensitivity to the ROSAT All Sky Survey allowing interesting sources to be identified by their long-term variability. Two different types of stellar sources are detected in shallow X-ray surveys: young stars (both pre-main and main sequence stars) and chromospherically active binaries (BY Dra and RS CVn type systems). The discovery of stars in such surveys and the study of their nature through optical follow-ups is valuable to determine their spatial distribution and scale height in the Galaxy. Our analysis shows that TYC 8380-1953-1 is a double-lined spectroscopic binary with both components having similar spectral type (likely K0/2+K3/5) and luminosity. With a typical coronal temperature for an RS CVn system ($kT \sim 1.15$ keV) and an X-ray luminosity in the $0.3-10$ keV energy band higher than $4 \times 10^{31}$ erg\,s$^{-1}$, TYC 8380-1953-1 lies among the most X-ray luminous RS CVn binaries.Comment: Accepted for publication in the PASP. 18 pages, 10 figure

Hadron Collider Signatures for New Interactions of Top and Bottom Quarks

One of the main goals for hadron colliders is the study of the properties of the third generation quarks. We study the signatures for new TeV resonances that couple to top or bottom quarks both at the Tevatron Run II and at the LHC. We find that in the simplest production processes of Drell-Yan type at the Tevatron, the signals are overwhelmed by QCD backgrounds. We also find that it is possible to study these resonances when they are produced in association with a pair of heavy quarks or in association with a single top at the LHC.In particular, with an integrated luminosity of 300 fb$^{-1}$ at the LHC, it is possible to probe resonance masses up to around 2 TeV.Comment: 24 pages, 15 figures, Minor corrections, version to appear in Phys. Rev.

Scalars from Top-condensation Models at Hadron Colliders

We study the production and decay of neutral scalars and pseudo-scalars at hadron colliders, in theories where the top-quark mass is the result of a $t\bar t$ condensate. We show that the dominant decay channel for masses below the $t\bar t$ threshold is the flavor changing mode $tc$. This is a consequence of the non-universal nature of the underlying interactions in all top-condensation models and provides a model-independent signature of these scenarios. We show that an upgraded Tevatron is sensitive to a sizeable region of the interesting parameter space and that the LHC will highly constrain these models through this flavor violating channel.Comment: 4 pages, 4 figures. Minor changes in figures for readibility. final version to appear in PR