Target Spin Research Articles

Funnel Landscape and Mutational Robustness as a Result of Evolution under Thermal Noise

Using a statistical-mechanical model of spins, the evolution of phenotype dynamics is studied. Configurations of spins and their interaction J represent the phenotype and genotype, respectively. The fitness for selection of J is given by the equilibrium spin configurations determined by a Hamiltonian with J under thermal noise. The genotype J evolves through mutational changes under selection pressure to raise its fitness value. From Monte Carlo simulations we find that the frustration around the target spins disappears for J evolved under temperature beyond a certain threshold. The evolved Js give the funnel-like dynamics, which is robust to noise and also to mutation.

Detection of glutamate and glutamine (Glx) by turbo spectroscopic imaging

Turbo spectroscopic imaging (TSI) is a spin echo spectroscopic imaging technique in which two or more echoes are acquired per excitation to reduce the acquisition time. The application of TSI has primarily been limited to the detection of uncoupled spins because the signal from coupled spins is modulated as a function of echo time. In this work we demonstrate how the TSI sequence can be modified to observe spins like the C 2 protons of Glx (≈3.75 ppm) which are involved solely in weak-coupling interactions. The technique exploits the chemical shift displacement effect by employing TSI refocusing pulses that have bandwidths which are less than the chemical shift difference between the target spins and the spins to which they are weakly coupled. The modified TSI sequence rewinds the J-evolution of the target protons in the slice of interest independently of the echo time or echo spacing, thereby removing any signal variation between successive echoes (apart from T 2 relaxation effects). In this study we tailored the narrow-bandwidth TSI sequence for observation of the C 2 Glx protons. The echo time was experimentally optimized to minimize signal contamination from myo-inositol, and the efficacy of the method was verified on phantom solutions of Glx and on brain in vivo.

HERMES Measurements of Hard-Exclusive Processes

Three HERMES measurements of hard-exclusive processes usefull for testing Generalized Parton Distributions (GPDs) are described. Firstly, Spin Density Matrix Elements (SDMEs) are determined from exclusive diffractive ρ0 and ϕ electroproduction in the HERMES experiment at 27.5 GeV beam energy. Then, Transverse Target Spin Asymmetry (TTSA) in exclusive ρ0 production and in Deeply Virtual Compton Scattering (DVCS) process on a transversally polarized hydrogen target is determined.

Transversity Measurements at COMPASS

The measurement of transverse spin effects in semi-inclusive deep-inelastic scattering is an important part of the COMPASS physics program. From the analysis of the 2002-2004 data, new results for the transverse target spin asymmetry of z-ordered identified pion and kaon pairs are presented. In addition, a first result for the transverse target spin asymmetry of exclusively produced ρ 0 mesons on the deuteron is shown.

First measurement of target and double spin asymmetries fore→p→→epπ0in the nucleon resonance region above theΔ(1232)

The exclusive channel polarized proton(polarized e,e prime p)pi0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the pi0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A_{1/2} and S_{1/2} for the Roper resonance N(1400)P11, and the N(1535)S11 and N(1520)D13 states.

Simultaneous adiabatic spin-locking cross polarization in solid-state NMR of paramagnetic complexes

Continuous-wave irradiations cross polarization and its variations had not been a popular choice for sensitivity enhancement in paramagnetic solids due to the large spectral broadening and the effect of fast relaxation on both the source and target spins. Furthermore, with the application of very-fast sample spinning, which is the prerequisite for high-resolution purposes, polarization transfer over a large bandwidth is further degraded. In this work, we report a wideband sensitivity enhancement in paramagnetic solid with our recently developed technique, simultaneous adiabatic spin-locking cross polarization, SADIS CP. Experiments were demonstrated with Cu(II)( d, l-alanine) 2 · H 2O under high-static field of 14.1 T and very-fast sample spinning of 31 kHz.

One-Step Implementation of Single Spin Measurement in Spin Star Network

We present an efficient one-step scheme for a single spin measurement based on nuclear magnetic resonance (NMR) techniques. This scheme considerably reduces the time of operation using a spin star network where a target spin and an ancillary spin are coupled to a ring of N spins. As opposed to the proposal in [Phys. Rev. Lett. 97(2006) 100501] using a cubic lattice crystal to achieve a cubic speedup, the distinct advantage of this scheme is that under ideal conditions it requires the application of only one step to create a system of N correlated spins. In the process of single spin measurement, the total macroscopic magnetization, the individual magnetization and the transfer fidelity are calculated analytically as simple cosine functions of time and the amplitude of irradiation.

New books

A simple criterion is defined which allows a quick estimate of a radar's capability to resolve two targets with differential motion. The criterion is applicable to general types of target motion, and hence will yield nominal resolution performance for arbitrary systems that utilize relative motion, such as synthetic aperture radar or inverse synthetic aperture radar, Doppler filters, systems that make use of target spin, and so forth. The criterion is considered both for weighted and unweighted signals.

Transverse target spin asymmetry in inclusive DIS with two-photon exchange

We study the transverse target spin dependence of the cross section for inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a ``partonlike'' mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark-helicity flip due to interactions with nonperturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, ${\ensuremath{\mu}}_{\mathrm{chiral}}^{2}\ensuremath{\gg}{\ensuremath{\Lambda}}_{\mathrm{QCD}}^{2}$. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order ${10}^{\ensuremath{-}4}$, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.

Transverse target spin asymmetry in exclusive [formula omitted] production

In this work we present the measurement of the transverse target spin asymmetry in the exclusive ρ 0 production using the COMPASS spectrometer at CERN. This will constitute an essential step to getting information about generalized parton distributions.

Exploiting the chemical shift displacement effect in the detection of glutamate and glutamine (Glx) with PRESS

A PRESS (Point RESolved Spectroscopy) sequence for the improved detection of the C 2 protons of Glx (glutamate and glutamine) at ≈3.75 ppm is presented in this work. It is shown that for spins like the C 2 protons of Glx which are involved solely in weak coupling interactions, the chemical shift displacement effect can be turned to advantage by exploiting PRESS refocusing pulses with bandwidths less than the chemical shift difference between the target spins and the spins to which they are weakly coupled. The narrow-bandwidth PRESS sequence allows refocusing of the J-coupling evolution of the target protons in the voxel of interest independently of echo time yielding signal equivalent to that which can be obtained with a one-pulse acquire sequence (assuming ideal pulses and ignoring T 2 relaxation). The total echo time of PRESS was set long enough for the decay of macromolecule signal and the two echo times were empirically optimized so that the Glx signal at 3.75 ppm suffered minimal contamination from myo-inositol. The efficacy of the method was verified on phantom solutions of Glx and on brain in vivo.

Generalized parton distributions and Deeply Virtual Compton Scattering on proton at CLAS

Two measurements of target and beam spin asymmetries for the reaction e p → e p γ were performed with CLAS at Jefferson Laboratory. Polarized 5.7 GeV electrons were impinging on a longitudinally polarized ammonia and liquid hydrogen target respectively. These measurements are sensitive to Generalized Parton Distributions. Sizable sin ϕ azimuthal angular dependences were observed in both experiments, indicating the dominance of leading twist terms and the possibility of extracting combinations of Generalized Parton Distributions on the nucleon.

Neutron transversity measurement at Jefferson Lab with a polarized 3He target

A first measurement of single target spin asymmetry (SSA) from semi-inclusive electroproduction of charged pions from a transversely polarized 3He target in deep-inelastic-scattering kinematics will take data in Hall A at Jefferson Lab in 2008. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. The experiment will be a coincidence measurement with the BigBite spectrometer detecting the scattered electrons and the left-arm HRS spectrometer detecting the charged pions. The prospect of future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is also discussed in this talk.

CONTROLLABLE ADIABATIC MANIPULATION OF THE QUBIT STATE

We propose a scheme which implements a controllable change of the state of the target spin qubit in such a way that both the control and the target spin qubits remain in their ground states. The interaction between the two spins is mediated by an auxiliary spin, which can transfer to its excited state. Our scheme suggests a possible relationship between the gate and adiabatic quantum computation.

Efficient cross polarization with simultaneous adiabatic frequency sweep on the source and target channels

In this work, we propose a new and efficient heteronuclear cross polarization scheme, in which adiabatic frequency sweeps from far off-resonance toward on-resonance are applied simultaneously on both the source and target spins. This technique, which we call as Simultaneous ADIabatic Spin-locking Cross Polarization (SADIS CP), is capable of efficiently locking both the source and target spins with moderate power even in the presence of large spectral distribution and fast relaxation. It is shown that by keeping the time-dependent Hartmann–Hahn mismatch minimal throughout the mixing period, polarization transfer can be accelerated. Experiments are demonstrated in a powder sample of l-alanine.

Numerical studies of International Linear Collider positron target and optical matching device field effects on beam

For an International Linear Collider (ILC) undulator-based positron source target configuration, a strong optical matching device (OMD) field is needed inside the target to increase the positron yield (by more than 40%) [Y. K. Batygin, Proceedings of the 2005 ALCPG and ILC Workshops, Snowmas, CO, 14–27 August 2005 (unpublished)] It is also required that the positron target be constantly rotated to reduce thermal and radiation damages. Eddy currents, produced by an OMD field in turn, interact with the magnetic field and produce a drag (stopping) force. This force not only produces heat in the disk but also creates a dipole deflecting field, which affects the beam. Therefore it is important to simulate such a system in detail to design the motor and cooling system and also a correction magnet system. In order to guide the ILC target design, an exact simulation of the spinning disk in a magnetic field is required. In this paper we present a simulation method implemented using COMSOL and compare it with the experimental results recently obtained at Stanford Linear Accelerator Center and Lawrence Livermore National Laboratory. Good agreement between the simulation and the experiment gives confidence in the validity of the method. We give detailed results on the proposed ILC target system, such as parametric studies for reduction of the power required to keep the target spinning. We present simulation results of the induced deflection field and of the reduction of the OMD field effect.

Incorporating homonuclear polarization transfer into PRESS for proton spectral editing: Illustration with lactate and glutathione

A proton spectral editing pulse sequence for the detection of metabolites with spin systems that involve weak coupling is presented. The sequence is based on homonuclear polarization transfer incorporated into the standard PRESS (Point RESolved Spectroscopy) sequence, which is a volume-selective double spin echo method, to enable spatial localization. All peaks in the region of interest are initially suppressed whether they are peaks from the target metabolite or from contaminating background. The target signal is then restored by polarization transfer from a proton that has a resonance outside the suppressed region and to which the target spins are weakly coupled. This is achieved by the application of a 90° hard pulse with phase orthogonal to that of the PRESS excitation pulse at the location of the first echo in PRESS and by optimizing the two PRESS timings, TE 1 and TE 2, for most efficient yield. Background signal not coupled to any protons outside the initially saturated region remains suppressed. The advantage of this sequence compared to multiple quantum filters is that signal from singlet peaks outside the suppressed area are preserved and can thus be used as a reference. The efficacy of the sequence was verified experimentally on phantom solutions of lactate and glutathione at 3.0 T. For the AX 3 spin system of lactate, the sequence timings were optimized by product operator calculations whereas for the ABX spin system of the cysteinyl group of glutathione numerical calculations were performed for sequence timing optimization.

ProtonGE/GMfrom beam-target asymmetry

The ratio of the proton's electric to magnetic form factor, G{sub E}/G{sub M}, can be extracted in elastic electron-proton scattering by measuring cross sections, beam-target asymmetry, or recoil polarization. Separate determinations of G{sub E}/G{sub M} by cross sections and recoil polarization observables disagree for Q{sup 2}>1 (GeV/c){sup 2}. Measurement by a third technique might uncover an unknown systematic error in either of the previous measurements. The beam-target asymmetry has been measured for elastic electron-proton scattering at Q{sup 2} = 1.51 (GeV/c){sup 2} for target spin orientation aligned perpendicular to the beam momentum direction. This is the largest Q{sup 2} at which G{sub E}/G{sub M} has been determined by a beam-target asymmetry experiment. The result, {mu}G{sub E}/G{sub M}=0.884{+-}0.027{+-}0.029, is compared to previous world data.

Solid State NMR Characterization of Nano-crystalline hydroxy-carbonate Apatite Using 1H-31P-13C Triple Resonance Experiments

AbstractThe local structure around hydrogen atoms, phosphate ions and carbonate ions in nano crystalline nonstoichiometric hydroxy-carbonate apatite was investigated in this study. The use of 13C enriched precursors allowed to perform 1D and 2D CP MAS HETCOR (HETeronuclear CORrelation) experiments with 13C as a target spin. 2D triple resonance experiments involving the 1H/13C/31P spins were also performed. All these experiments led to the partial editing of the corresponding projection spectra and revealed fine structural details for the corresponding material. At least four 13C peaks, corresponding to carbonate ions in A sites (OH-) and B-sites (PO43-) were evidenced.

New Local System of Measurement of Axial Strains for Triaxial Apparatus Using LVDT

Abstract This paper presents a new local system of measurement of axial strains for triaxial apparatus using LVDT. The bodies of four nonsubmersible transducers are supported by an independent circular ring, while the rods are simply put on local targets (pins pushed through the membrane into the sample). A flexible metal plate is used to attach the body of the LVDT to the circular ring and a nonrigid connection is considered between the rod and the pin. These original developments allow the system to investigate the soil behavior in large strains, up to 15 × 10−2 m/m, and to accommodate the radial deformation, tilting, and usually inevitable barreling of the sand specimen. The soil stiffness in the small strain domain, less than some 10−5 m/m, can be evaluated with good accuracy, as well as its evolution during triaxial compression or extension tests. The assessment of errors is discussed and the performance of the device is shown with results of tests on Hostun RF sand.