Communication: Partial polarization transfer for single-scan spectroscopy and imaging

A method is presented to partially transfer nuclear spin polarization from one isotope S to another isotope I by the way of heteronuclear spin couplings, while minimizing the loss of spin order to other degrees of freedom. The desired I spin polarization to be detected is a design parameter, while the sequence of pulses at the two Larmor frequencies is optimized to store the greatest unused S spin longitudinal polarization for subsequent use. The unitary evolution for the case of I_NS spin systems illustrates the potentially ideal efficiency of this strategy, which is of particular interest when the spin-lattice relaxation time of S greatly exceeds that of I. Explicit timing and pulses are tabulated for the cases for which M ≤ 10 partial transfers each result in equal final polarization of 1/M or more compared to the final I polarization expected in a single transfer for N = 1, 2, or 3 I spins. Advantages for the ratiometric study of reacting molecules and hyperpolarized initial conditions are outlined

Functional characterization of spatial neglect in Parkinson's disease

Parkinson’s disease (PD) is associated with perceptual as well as motor disturbances. Unlike those with right-side onset (RPD), individuals whose motor symptoms begin on the left side of the body (LPD) may experience mild neglect of left hemispace. The functional cause of these perceptual abnormalities in LPD is unknown; possibilities include altered eye movements, changes in perceptual representation of left versus right hemispace, and attentional abnormalities. Three studies explored these possibilities in non-demented individuals with mild-moderate idiopathic PD (24-36 per experiment) and matched normal control adults (NC; 14-24 per experiment). Study 1 consisted of two psychophysical line-bisection experiments that used brief stimulus presentations to preclude exploratory eye movements. In both, participants judged whether a systematically adjusted hatchmark was left or rightward of a horizontal line’s midpoint. In the second, eye tracking was used to ensure that participants fixated during stimulus onset. The first experiment revealed neglect-like performance in LPD, but the second did not, suggesting that neglect may arise from biased eye gaze but not from abnormal saccades. Study 2 evaluated two hypotheses to explain spatial bias in LPD; one an active hypothesis in the literature that the representation of left hemispace is compressed, and the other a novel hypothesis that left hemispace is less salient than the right in LPD. Both hypotheses were assessed psychophysically, using spatial frequency and contrast discrimination paradigms, and neither was supported. Study 3 investigated whether endogenous visuospatial attentional abnormalities exist in PD, and particularly whether LPD show weaker attentional abilities in the left hemifield. A multiple-object tracking paradigm was used along with eye tracking to ensure that participants used only endogenous (not exogenous) attention. PD showed dilated temporal resolution of attention, and were less accurate in tracking multiple objects at once. LPD did not differ from RPD for either of these metrics. Overall the results suggest that there is no intrinsic difference in the representation of space in LPD relative to RPD or NC, but that visuospatial attention is altered in PD generally. The latter finding is particularly important for considering spatial navigation in individuals with PD even in early stages of the disease

Nanoscale Torsional Resonator for Polarization and Spectroscopy of Nuclear Spins

We propose a torsional resonator that couples to the transverse spin dipole of an attached sample. The absence of relative motion eliminates a source of friction that would otherwise hinder nanoscale implementation. Enhanced spontaneous emission induced by the resonator relaxes the longitudinal spin dipole at a rate of ~1  s^(-1) in the low-temperature limit. With signal averaging, single-proton magnetic resonance spectroscopy appears feasible at ~10  mK and a high magnetic field, while single-shot sensitivity is practical for samples with at least tens of protons in a volume of ~5  nm^3

Normal discrimination of spatial frequency and contrast across visual hemifields in left-onset Parkinson’s disease: evidence against perceptual hemifield biases

Individuals with Parkinson's disease (PD) with symptom onset on the left side of the body (LPD) show a mild type of left-sided visuospatial neglect, whereas those with right-onset (RPD) generally do not. The functional mechanisms underlying these observations are unknown. Two hypotheses are that the representation of left-space in LPD is either compressed or reduced in salience. We tested these hypotheses psychophysically. Participants were 31 non-demented adults with PD (15 LPD, 16 RPD) and 17 normal control adults (NC). The spatial compression hypothesis was tested by showing two sinusoidal gratings, side by side. One grating's spatial frequency (SF) was varied across trials, following a staircase procedure, whereas the comparison grating was held at a constant SF. While fixating on a central target, participants estimated the point at which they perceived the two gratings to be equal in SF. The reduced salience hypothesis was tested in a similar way, but by manipulating the contrast of the test grating rather than its SF. There were no significant differences between groups in the degree of bias across hemifields for SF discrimination or for contrast discrimination. Results did not support either the spatial compression hypothesis or the reduced salience hypothesis. Instead, they suggest that at this perceptual level, LPD do not have a systematically biased way of representing space in the left hemifield that differs from healthy individuals, nor do they perceive stimuli on the left as less salient than stimuli on the right. Neglect-like syndrome in LPD instead presumably arises from dysfunction of higher-order attention.Published versio

Weather Index Insurance and the Pricing of Spatial Basis Risk

Agricultural Finance,