The clinical importance of measurement of the regional cerebral hemodynamics, using positron emission tomography (PET) or single-photon emission computed tomography (SPECT), is to ascertain the viability of the ischemic tissue or to predict the functional outcome after ischemic cerebral vascular diseases. Specifically, the following aspects may be considered important: I) to determine the state of the hemodynamics in regions of the brain identified from clinical signs and symptoms as ischemic or infarcted, 2) to determine whether the local flow is sufficient or at risk, 3) to estimate the prognosis with or without intervention and 4) to assess whether the risk of a second post-acute infarction has been reduced after treatment. In addition to investigations of the regional cerebral blood flow (CBF), there is now a growing interest in the role of the cerebral blood volume (CBV) and blood viscosity in the pathophysiology of cerebral ischemia. Recent studies have focused on the effectiveness of hemorheological approaches, including hemodilution ther­ apy, in the treatment of cerebral vascular diseases [1]. Employing PET, Gibbs et al. [2] and Powers et al. [3] suggested that the cerebral mean transit time derived from the ratio between CBF and CBV might serve as a sensitive parameter for estimating the circulatory reserve in the ischemic tissue. In the present study, SPECT was used to measure the regional CBF, CBV and cerebral hematocrit in normals and patients with occlusive cerebral vascular dis­ eases. Based on these three cerebral hemodynamic parameters, the regional patho­ physiology during the acute stages of cerebral infarction and of transient ischemic attack (TIA) was evaluated.

The fundamental building blocks of the proton-quarks and gluons-have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and their dynamics give rise to the quantum bound state of the proton and its physical properties, such as its spin¹. The two up quarks and the single down quark that comprise the proton in the simplest picture account only for a few per cent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force². An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter-antimatter quark pairs inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks within protons difficult to study, but their existence is discernible in reactions in which a matter-antimatter quark pair annihilates. In this picture of quark-antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, given that their masses are very similar and small compared to the mass of the proton³. Here we provide evidence from muon pair production measurements that these distributions are considerably different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momenta. These results are expected to revive interest in several proposed mechanisms for the origin of this antimatter asymmetry in the proton that had been disfavoured by previous results⁴, and point to future measurements that can distinguish between these mechanisms.

In Fig. 1c of this Article, the x-axis scale was inadvertently duplicated from Fig. 1b. The original Article has been corrected online.

We report the p+p and p+d differential cross sections measured in the SeaQuest experiment for J/ψ and ψ(2S) production at [Formula presented] beam energy covering the forward x-Feynman (xF) range of 0.5

Evidence for a flavor asymmetry between the ū and d¯ quark distributions in the proton has been found in deep-inelastic scattering and Drell-Yan experiments. The pronounced dependence of this flavor asymmetry on x (fraction of nucleon momentum carried by partons) observed in the Fermilab E866 Drell-Yan experiment suggested a drop of the d¯(x)/ū(x) ratio in the x>0.15 region. We report results from the SeaQuest Fermilab E906 experiment with improved statistical precision for d¯(x)/ū(x) in the large x region up to x=0.45 using the 120 GeV proton beam. Two different methods for extracting the Drell-Yan cross section ratios, σpd/2σpp, from the SeaQuest data give consistent results. The d¯(x)/ū(x) ratios and the d¯(x)-ū(x) differences are deduced from these cross section ratios for 0.13

The SeaQuest spectrometer at Fermilab was designed to detect oppositely-charged pairs of muons (dimuons) produced by interactions between a 120 GeV proton beam and liquid hydrogen, liquid deuterium and solid nuclear targets. The primary physics program uses the Drell–Yan process to probe antiquark distributions in the target nucleon. The spectrometer consists of a target system, two dipole magnets and four detector stations. The upstream magnet is a closed-aperture solid iron magnet which also serves as the beam dump, while the second magnet is an open aperture magnet. Each of the detector stations consists of scintillator hodoscopes and a high-resolution tracking device. The FPGA-based trigger compares the hodoscope signals to a set of pre-programmed roads to determine if the event contains oppositely-signed, high-mass muon pairs.