Dark Matter Search Results from the PICO-60 C_{3}F_{8} Bubble Chamber.

New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C_{3}F_{8} located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, PICO-60 C_{3}F_{8} exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than one event per month. A blind analysis of an efficiency-corrected 1167-kg day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the weakly interacting massive particle (WIMP)-proton spin-dependent cross section at 3.4×10^{-41} cm^{2} for a 30-GeV c^{-2} WIMP, more than 1 order of magnitude improvement from previous PICO results.

Dark Matter Search Results from the PICO-2L C3F8 Bubble Chamber.

New data are reported from the operation of a 2 liter C3F8 bubble chamber in the SNOLAB underground laboratory, with a total exposure of 211.5 kg days at four different energy thresholds below 10 keV. These data show that C3F8 provides excellent electron-recoil and alpha rejection capabilities at very low thresholds. The chamber exhibits an electron-recoil sensitivity of <3.5×10(-10) and an alpha rejection factor of >98.2%. These data also include the first observation of a dependence of acoustic signal on alpha energy. Twelve single nuclear recoil event candidates were observed during the run. The candidate events exhibit timing characteristics that are not consistent with the hypothesis of a uniform time distribution, and no evidence for a dark matter signal is claimed. These data provide the most sensitive direct detection constraints on WIMP-proton spin-dependent scattering to date, with significant sensitivity at low WIMP masses for spin-independent WIMP-nucleon scattering.

Low-temperature magnetic circular dichroism spectra and magnetisation curves of 4Fe clusters in iron-sulphur proteins from Chromatium and Clostridium pasteurianum.

The magnetic circular dichroism (MCD) spectra of the 4Fe clusters in the iron-sulphur proteins high-potential iron protein from Chromatium and the 8Fe ferredoxin from Clostridium pasteurianum have been measured over the wavelength range 300-800 nm at temperatures between approx. 1.5 and 50 K and at magnetic fields up to 5 tesla. In both cases the proteins have been studied in the oxidized and reduced states. The reduced state of high-potential iron protein gives a temperature-independent MCD spectrum up to 20 K, confirming the diamagetism of this state at low temperature. The MCD spectrum of samples of oxidized ferredoxin invariably show the presence of a low concentration of a paramagnetic species, in agreement with the observation that the EPR spectrum always shows a signal at g = 2.01. The paramagnetic MCD spectrum runs across the whole of the wavelength range studied and therefore most probably originates from an iron-sulphur centre. The diamagnetic component of the MCD spectrum of oxidized ferredoxin is very similar to that of reduced high-potential iron protein. The low-temperature MCD spectra of oxidized high-potential iron protein and reduced ferredoxin reveal intense, temperature-dependent bands. The spectra are highly structured with that of high-potential iron protein showing a large number of electronic transitions across the visible region. The MCD spectra of the two different oxidation levels are quite distinctive and should provide a means of establishing the identity of these state of 4Fe clusters in more complex proteins. MCD magnetisation curves have been constructed from detailed studies of the field and temperature dependence of the MCD spectra of the two paramagnetic oxidation states. These plots can be satisfactorily fitted to the theoretically computed curves for an S = 1/2 ground state with the g factors experimentally determined by EPR spectroscopy. The low-temperature MCD spectra of the reduced 2Fe-2S ferredoxin from Spirulina maxima are also presented and MCD magnetisation curves plotted and fitted to the experimentally determined g factors.

The three-iron cluster in a ferredoxin from Desulphovibrio gigas. A low-temperature magnetic circular dichroism study.

Ferredoxin II from Desulphovibrio gigas is a tetrameric protein containing a novel iron-sulphur cluster consisting of three iron atoms. The low-temperature magnetic circular dichroism (MCD) spectra of the oxidized and dithionite-reduced forms of ferredoxin II have been measured over the wavelength range approx. 300-800 nm. Both oxidation levels of the cluster are shown to be paramagnetic, although only the oxidized form gives an EPR signal. MCD magnetization curves have been constructed over the temperature range approx. 1.5-150 K and at fields between 0 and 5.1 Tesla. The curve for the oxidized protein can be fitted to a ground state of spin S = 1/2 with an isotropic g factor of 2.01. There is evidence for the thermal population of a low-lying electronic state above 50 K. The reduced protein gives a distinctive set of magnetization curves that are tentatively assigned to a ground state of S = 2, with a predominantly axial zero-field distortion that leaves the doublet Ms = +/-2 lowest in energy. The zero-field components have a maximum energy spread of approx. 15 cm-1. which places an upper limit of 4 cm-1 on the axial zero-field parameter D. The MCD spectra of the oxidized and reduced forms of the cluster are quite distinctive from one another. The spectra of the oxidized state are also different from those of oxidized high-potential iron protein from Chromatium and should provide a useful criterion for distinguishing between four- and three-iron clusters in their highest oxidation levels.

Determination of left-ventricular volume from first-pass kinetics of labeled red cells.

A mathematical model is presented for the dynamics of a bolus of technetium-99m-labeled red blood cells through the left ventricle. It is used to correct for attenuation the count rate observed over the left ventricle during a conventional gated blood-pool study. The left-ventricular volumes are calculated from the corrected count rates and expressed as a percentage of total blood volume, or in absolute terms if a blood sample is obtained. The procedure is applied to a number of patients with nonvalvular cardiac disease. Cardiac volumes determined by the method are found to correlate well (r = 0.98) with those determined by contrast left ventriculography. The method is simple, requires no special equipment, and can be applied with existing computer software.

Flank mass and pain in a 72-year-old man.

This patient had retroperitoneal multiseptated masses, which extensively invaded the right flank and thigh musculature. The radiologic, pathologic, and clinical findings were consistent with a retroperitoneal pseudomyxoma from an appendiceal mucocele.

The diagnosis of herniated intervertebral disks with MR imaging: a comparison of gradient-refocused-echo and spin-echo pulse sequences.

Axial MR images of 65 lumbar disks with herniated nucleus pulposus imaged by gradient-refocused-echo (GRE) and spin-echo (SE) MR pulse sequences of 200-400/15 with a flip angle of 15-30 degrees was selected as optimal because of its high signal-to-noise ratio and good contrast between CSF, nucleus pulposus, and bone. The GRE technique was confirmed to be more sensitive in detecting prolapsed disks than the SE technique, but was less sensitive in demonstrating extruded disks. The combination of axial GRE and SE resulted in high detectability of herniated nucleus pulposus on axial MR images. Our results suggest that the GRE technique is an important adjunct to SE imaging in studying herniated nucleus pulposus.

The distribution of amylobarbitone, butobarbitone, pentobarbitone and quinalbarbitone and the hydroxylated metabolites in man.

Fluid and tissue specimens collected from 30 subjects at autopsy have been assayed for their content of common sedative barbiturates and the corresponding hydroxylated metabolites by g.l.c. Where one barbiturate had been ingested an inverse relationship between lipid solubility of the drug and the distribution in fluids and tissues was observed. In most cases the liver, and in the remainder the spleen, contained the highest concentrations of barbiturate. Bile concentrations were often in excess of those in the corresponding liver. The metabolites of the four sedative barbiturates were usually present in lower amounts than the parent drugs in the fluids and tissues of most subjects but urine often contained much higher concentrations of metabolites--sometimes exceeding that of the parent drug in the liver. Administration of two or more barbiturates together did not appear to affect the distribution and metabolism of the individual drugs.

The human distribution of some barbiturate sedatives in combination with miscellaneous CNS-active drugs.

This paper presents 14 cases in which the distribution of barbiturates and the hydroxylated metabolites in combination with miscellaneous CNS-active drugs was studied. In 7 of these cases the other drug present was methadone, and in the remainder dihydrocodeine, morphine, propoxyphene, amitriptyline, meprobamate, cyclizine and dipipanone, diphenhydramine and methaqualine. Amitriptyline, methadone, cyclizine and dipipanone, methaqualone and diphenhydramine appeared to modify the distribution of amylorbarbitone and quinalbarbitone. Likewise, the barbituates seemed to alter the distribution of amitriptyline, propoxyphene and, in one instance, methadone.

Melanoma metastatic to the bronchus: radiologic features in two patients.

Two patients with cutaneous melanoma metastatic to the bronchus are described. Chest radiographs revealed only indirect signs of bronchial obstruction. Computed tomography (CT) clearly demonstrated the intraluminal lesion. Magnetic resonance (MR) imaging signal characteristics were not specific for melanoma.

Degenerative lumbar spine disorders in gradient refocused echo axial magnetic resonance images.

The axial images of 58 lumbar disks having degenerative disorders imaged by gradient refocused echo (GRE) and spin echo (SE) magnetic resonance imaging (MRI) pulse sequences at high field strength were compared for diagnostic quality. The vacuum phenomenon, calcified disk, and bony hypertrophic changes were better demonstrated by GRE images than by SE images due to magnetic susceptibility effect. Axial GRE images are therefore useful adjuncts to SE images for effective MRI of degenerative lumbar spine disorders at high field strength.

Distribution of joint effusion in patients with traumatic knee joint disorders: MRI assessment.

One hundred forty-five knee magnetic resonance imaging examinations with joint effusions were reviewed to clarify the usual distribution of joint fluids in patients with traumatic knee joint disorders. Almost all knees (99%) had effusions in the central portion, and most knees (76%) had effusions in the suprapatellar pouch. Effusions were rarely found in the posterior femoral recess (9%) or subpopliteal recess (2%). However, this difference was considered to be only a reflection of anatomic communications. Effusions were occasionally found around posterior cruciate ligaments (36%), but were less frequently seen around anterior cruciate ligaments (18%).

Peripheral findings in MR using surface coil.

Incidental peripheral lesions found during neuroradiological MR examinations with surface coils are reviewed. These include intracranial metastases during orbital examinations, cerebellar and thyroid lesions during cervical spine examinations, and dissecting and saccular abdominal aneurysms, as well as renal and intrapelvic abnormalities during lumbar spine examinations. Because of the reduced field-of-view and rapid signal drop-off in deeper portions of the body when examinations are performed with surface coils, peripheral and deep regions also need careful attention during routine evaluation.

Computed tomographic and magnetic resonance imaging of vanishing cerebral infarct.

A thalamic infarct in a 65-year-old woman was initially imaged as a discrete low-density mass in the left side of her thalamus by CT. Abnormal MR signal was also noted in the thalamus and midbrain. Follow-up imaging showed nearly complete resolution of the low-density lesion on CT and the abnormal signal on MR.

Leiomyosarcoma after retinoblastoma radiotherapy.

The CT and MR appearance of leiomyosarcoma in the left orbit in a 15-year-old girl is presented. This tumor developed after successful radiation therapy for bilateral retinoblastoma.

[Abnormal gas collections in the abdomen in infants]. / Epanchements gazeux anormaux de l'abdomen du nourrisson.

Many unusual and uncommon abnormal gas collections within the abdomen may be encountered. This paper reviews the reported causes for unusual gas collections in the abdomen and describes several new causes of abnormal bowel gas collections.