Characteristics of zero-quantum correlation spectroscopy in MAS NMR experiments

Zero-quantum coherence generation and reconversion in magic-angle spinning solid-state NMR is analyzed. Two methods are discussed based on implementations using symmetry-based pulse sequences that utilize either isotropic J couplings or dipolar couplings. In either case, the decoupling of abundant proton spins plays a crucial role for the efficiency of the zero-quantum generation. We present optimized sequences for measuring zero-quantum single-quantum correlation spectra in solids, achieving an efficiency of 50% in ubiquitin. The advantages and disadvantages of zero-quantum single-quantum over single-quantum single-quantum correlation spectroscopy are explored, and similarities and differences with double-quantum single-quantum correlation spectroscopy are discussed. Finally, possible application of zero-quantum single-quantum experiments to polypeptides, where it can lead to better spectral resolution is investigated using ubiquitin, where we find high efficiency and high selectivity, but also increased line widths in the MQ dimension.     

Time-resolved stimulated emission spectroscopy in the ultrashort domain through pump-probe experiments

The photoemission properties of fluorescent chromophores have a widespread application in many fields ranging from chemical-physics and biology to organic light emitting devices. These systems usually display high fluorescence conversion efficiency, which makes them suitable for transient/gain experiments also in liquid solutions, thin films and eventually in protein environments.Pump and probe methods have been widely employed for wavelength-resolved spectroscopy in the subpicosecond time scale. In our group, we have recently assembled a new experimental setup for pump and probe spectroscopy: preliminary tests on the Rhodamine B dye in ethanol have been performed in order to optimize the setup. The dynamic response of photoinduced changes of the chromophore dispersed into a suitable solvent has been studied with a subpicosecond time resolution.The optically prepared initial state of the Rhodamine B in ethanol solution appears to evolve on a timescale of few picoseconds into a successive state, which could be attributed to an intramolecular charge transfer state.     

Increasing hydrodynamic efficiency by reducing cross-beam energy transfer in direct-drive-implosion experiments

A series of experiments to determine the optimum laser-beam radius by balancing the reduction of cross-beam energy transfer (CBET) with increased illumination nonuniformities shows that the hydrodynamic efficiency is increased by ～35%, which leads to a factor of 2.6 increase in the neutron yield when the laser-spot size is reduced by 20%. Over this range, the absorption is measured to increase by 15%, resulting in a 17% increase in the implosion velocity and a 10% earlier bang time. When reducing the ratio of laser-spot size to a target radius below 0.8, the rms amplitudes of the nonuniformities imposed by the smaller laser spots are measured at a convergence ratio of 2.5 to exceed 8 μm and the neutron yield saturates despite increasing absorbed energy, implosion velocity, and decreasing bang time. The results agree well with hydrodynamic simulations that include both nonlocal and CBET models.     

Increasing the rewriting speed of optical rewritable e-paper by selecting proper liquid crystals

The effect of interaction between liquid crystal(LC) and photoalignment material on the speed of optical rewriting process is investigated.The theoretical analysis shows that a smaller frank elastic constant K 22 of liquid crystal corresponds to a larger twist angle,which gives rise to a larger rewriting speed.Six different LC cells with the same boundary conditions(one substrate is covered with rubbed polyimide(PI) and the other with photo sensitive rewritable sulfuric dye 1(SD1)) are tested experimentally under the same illumination intensity(450 nm,80 mW/cm 2).The results demonstrate that with a suitable liquid crystal,the LC optical rewriting speed for e-paper application can be obviously improved.For two well known LC materials E7(K22 is larger) and 5CB(K22 is smaller),they require 11 s and 6 s corresponding to change alignment direction for generating image information.     

Increasing the rewriting e-paper by selecting speed of optical rewritable proper liquid crystals

The effect of interaction between liquid crystal （LC） and photoalignment material on the speed of optical rewriting process is investigated. The theoretical analysis shows that a smaller frank elastic constant K22 of liquid crystal corresponds to a larger twist angle, which gives rise to a larger rewriting speed. Six different LC cells with the same boundary conditions （one substrate is covered with rubbed polyimide （PI） and the other with photo sensitive rewritable sulfuric dye I（SD1）） are tested experimentally under the same illumination intensity （450 nm, 80 mW/cm2）. The results demonstrate that with a suitable liquid crystal, the LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 （K22 is larger） and 5CB （K22 is smaller）, they require 11 s and 6 s corresponding to change alignment direction for generating image information.     

Double resonance experiments in57Fe Mössbauer spectroscopy

Splitting of Mössbauer lines has been observed in conventional energy domain spectra of Permalloy samples when an external radio frequency (rf) magnetic field was tuned to be in resonance with the separation of Zeeman sublevels of either the ground or the excited state of the⁵⁷Fe nucleus. Time domain measurements were performed with the frequency of the rf field close to the natural linewidth of the 14.4 keV Mössbauer state. A nonmagnetostrictive magnetically soft Permalloy sample was used in the experiments.     

Effects of modulation on signals obtained in saturated absorption spectroscopy experiments

An analysis of the useful signals detected in saturated absorption spectroscopy experiments is given. Both Gaussian and plane-wave fields are considered. The various cases of unmodulated, square-wave modulated and sinusoidally modulated saturating beams are examined. It is found that square-wave and sinusoidal modulations give different results. The first is identical to no modulation, and detection at the fundamental frequency records a fraction of the total signal which is also a square wave. The second gives fundamental or higher-harmonic signals each with a very different dependence on the saturation parameter. The signal at the fundamental saturates faster and more completely than that for square-wave modulation. The results suggest experimental methods for the determination of the absolute value of the saturation parameter.     

Observation of heterodyne mixing in surface x-ray photon correlation spectroscopy experiments

We report measurements of propagating capillary waves on a liquid water surface at T=5 degrees C with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the q region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions g(1)(tau) and g(2)(tau).     

Shear wave speed recovery using moving interference patterns obtained in sonoelastography experiments

Two new experiments were created to characterize the elasticity of soft tissue using sonoelastography. In both experiments the spectral variance image displayed on a GE LOGIC 700 ultrasound machine shows a moving interference pattern that travels at a very small fraction of the shear wave speed. The goal of this paper is to devise and test algorithms to calculate the speed of the moving interference pattern using the arrival times of these same patterns. A geometric optics expansion is used to obtain Eikonal equations relating the moving interference pattern arrival times to the moving interference pattern speed and then to the shear wave speed. A cross-correlation procedure is employed to find the arrival times; and an inverse Eikonal solver called the level curve method computes the speed of the interference pattern. The algorithm is tested on data from a phantom experiment performed at the University of Rochester Center for Biomedical Ultrasound.     

Solid-state NMR spectroscopy using the lost I spin magnetization in polarization transfer experiments

A variation of the cross polarization (CP) experiment is discussed. The method requires two scans where the difference signal is equivalent to the I spin magnetization that is transferred to the S spins. The acquired signal is equivalent to F1 sum projection of a two-dimensional (2D) heteronuclear correlation experiment and is obtained by just two scans without the need to increment the indirect time domain t(1). Any polarization transfer method and any kind of spin manipulations during the t(1) incrementation period of a 2D NMR experiment can be applied. The method allows fast measurements of the CP transfer, particularly if various S spins signal overlap and is good for spectral editing of I spin signals with contact to S spins. Various examples for biomaterials are presented. Most importantly, this novel approach is ideal for detailed investigations of organic-mineral interfaces in bone, here demonstrated for O-phospho-l-serine as simple model compound.     

Role of strong correlation in the recent angle-resolved photoemission spectroscopy experiments on cuprate superconductors

Motivated by recent photoemission experiments on cuprates, the low-lying excitations of a strongly correlated superconducting state are studied numerically. It is observed that along the nodal direction these low-lying one-particle excitations show a linear momentum dependence for a wide range of excitation energies and, thus, they do not present a kinklike structure. The nodal Fermi velocity v(F), as well as other observables, are systematically evaluated directly from the calculated dispersions, and they are found to compare well with experiments. It is argued that the parameter dependence of v(F) is quantitatively explained by a simple picture of a renormalized Fermi velocity.     

Increasing rewriting speed of optical rewritable e-paper by selecting proper liquid crystals

Effect of interaction between liquid crystal (LC) and photoalignment material on speed of optical rewriting process is investigated. The theoretical analysis shows that smaller frank elastic constant K₂₂ of liquid crystal corresponds to larger twist angle, which gives rise to larger rewriting speed. Six different LC cells with the same boundary conditions (one substrate is covered with rubbed polyimide (PI) and other with photo sensitive rewritable sulfuric dye 1(SD1)) are tested experimentally under the same illumination intensity (450 nm, 80 mW/cm²). The results demonstrate that with suitable liquid crystal, LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 (K₂₂ is larger) and 5CB (K₂₂ is smaller), they require 11 s and 6 s corresponding to change alignment direction for generating image information.     

Doppler-dependent fluorescence spectroscopy of Yb atomic gas for trapped-ion experiments

An ion trap-based Quantum system has been one of the leading architectures toward building a scalable and practical quantum computer. The trapped ion system also has been used for precision experiments such as quantum sensing, metrology, and atomic clock. For the ion-trap experiment, searching resonant frequencies of atomic isotopes are essential for selectively ionization and trapping a specific isotope. In this work, we set up an Yb fluorescence spectroscopy for detecting 399 nm photons of ¹S₀ → ¹P₁ transition of the Yb gas from a heated oven. We observed the relative frequency differences between the Yb isotopes and calibrated an optical wavemeter comparing with previous literatures. In addition, we obtain characteristic properties of the atomic oven such as gas’ velocity and density distribution at different oven temperatures. Our experiment can offer a relatively simple and cost-efficient apparatus of spectroscopy and can be useful for designing trap devices in the trapped-ion experiment.     

Increasing the sensitivity of time-resolved photo-CIDNP experiments by multiple laser flashes and temporary storage in the rotating frame

Pulse sequences have been developed that add up time-resolved photo-CIDNP signals from n successive laser flashes not in the acquisition computer of the NMR spectrometer but in the experiment itself, resulting in a greatly improved signal-to-noise ratio. For this accumulation, CIDNP is first stored in the transverse plane and then on the z axis, and finally superimposed on CIDNP produced by the next flash. These storage cycles also result in a very efficient background suppression. Because only one free induction decay is acquired for n flashes, the noise is digitized only once. The signal gain is demonstrated experimentally and analyzed theoretically. Losses are mostly due to nuclear spin relaxation, and to a small extent to instrument imperfections. With 10 laser flashes, a signal increase by a factor of about 7.5 was realized. As their main advantage compared to signal averaging in the usual way, these sequences yield the same signal-to-noise ratio with fewer laser flashes; the theoretical improvement is by a factor of n.     

Increasing the sensitivity of cryoprobe protein NMR experiments by using the sole low-conductivity arginine glutamate salt

Decrease in experimental sensitivity of cryoprobe experiments for salty samples, attributed to increased sample conductivity, has been a long-standing issue in protein NMR. Salt concentration can not be simply reduced as this often leads to protein aggregation. A simple and inexpensive solution to this problem is demonstrated here. We show that even for proteins prone to aggregation, the traditional solubilizing salt, 100mM NaCl, can be completely replaced by 50mM l-Arg and l-Glu. This replacement simultaneously reduces the sample conductivity and improves protein solubility. Up to a 6-fold overall increase in experimental sensitivity was achieved, in comparison with the traditional salty buffer. At constant protein concentration up to 2-fold increase in sensitivity was observed. The lengths of the proton pi/2 pulses were also significantly decreased, up to the level typical for non-salty samples in water.     

Express analysis of spectra in precision experiments

Some precision experiments require several tens of hours for measurements. In this case, it is important to take into account possible drift of the detection system parameters in time. An express analysis program has been developed for early detection of significant distortions in recorded spectra, their filtration, and correction of results. Original Russian Text ? N.A. Gundorin, N.D. Dikoussar, N.G. Maznyj, L.B. Pikelner, I.M. Salamatin, M.I. Tsulaja, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 2, pp. 261–263.