Hall and drift mobilities in molecular beam epitaxial grown GaAs

A series of nominally undoped and Si-doped GaAs samples have been grown by molecular beam epitaxy (MBE) with Hall concentrations ranging from 10¹⁵ to 10¹⁹ cm⁻³ and mobilities measured at 77 and 300K by Hall-van der Pauw methods. Drift mobilities were calculated using the variational principle method and Hall scattering factors obtained from a relaxation-time approximation to permit cross-correlation of experimental data with drift or Hall mobilities and actual or Hall electron concentrations. At 77K, both high purity and heavily doped samples are well represented by either drift or Hall values since piezoelectric acoustic phonon scattering and strongly screened ionized impurity scattering hold the Hall factor close to unity in the respective regimes. Between n≊10¹⁵ and 10¹⁷ cm⁻³, where lightly screened ionized impority scattering predominates, Hall mobility overestimates drift mobility by up to 50 percent and Hall concentration similarly underestimates n. At 300K, polar optical phonons limit mobility and a Hall factor up to 1.4 is found in the lowest doped material, falling close to unity above about 10¹⁶ cm⁻³. Our calculation also agrees remarkably well with the Hall mobility of the highest purity MBE grown sample reported to date.     

Inhibition of feline collateral vessel development following experimental thrombolic occlusion

We compared development of feline hindlimb collateral circulation after acute occlusion of the terminal aorta by ligation, thrombus formation, and formation of a "closed" aortic loop containing thromboplastin. Collateral circulation development was assessed by aortograms, scintillation scans, neurological signs following occlusion, measurement of hindlimb muscle blood flow, and forelimb and hindlimb temperature. In cats in which aortic occlusion was the result of ligation or thromboplastin in the aortic loop, paralysis was not evident. Aortograms and scintillation scans indicated hindlimb blood flow. Both muscle temperature and blood flow data indicated that the return of blood flow was rapid. The 5th lumbar artery appears to be the origin of the collateral vessels. The mid-zone component is a dorsal and ventral vertebral route and an epaxial muscle route. The reentry components are the 6th or 7th lumbar arteries. The collateral vessels arise from preexisting collateral vessels. Of those cats in which aortic occlusion was the result of a thrombus, all exhibited paralysis. Aortograms, scintillation scans, muscle temperature, and hindlimb blood flow data indicated reduced hindlimb blood flow. The results suggest that the thrombus has an inhibitory effect on the development of collateral circulation.     

A new approach to the treatment of renal failure

There is an apparent need for an alternative form of treatment for renal failure. This study, therefore, sought to determine the feasibility of dialysing across an isolated loop of colon and its possible application to augment failing renal function in chronic uraemic patients. Haemodialysis and renal transplantation are undisputedly effective in treating renal failure but have many drawbacks. They are unavailable in the underdeveloped world, extremely expensive to institute and maintain, and their need and expense are compounded every year by the discovery of new cases. Colonic loops were isolated in sheep and studies performed to find an effective solution in terms of urea clearance. The best solution was then used in animals in which acute or chronic uraemia was induced and, compared with controls, prolonged life significantly (P less than 0-05). Once it had been established that urea could be removed across the colonic mocosa, it was used in patients with established isolated loops of colon. Even though they had normal blood levels, urea was recovered in the dialysate. Results indicate that colonic dialysis, which is simple and inexpensive, may have a place as an adjunctive therapy in the treatment of chronic renal failure.     

Incomplete dominance of the gene for naked neck in domestic fowl

The autosomal gene for naked neck in domestic fowl has been shown to be incompletely dominant. Heterozygotes characteristically have an isolated tuft of feathers on the ventral side of the neck above the crop. Homozygotes lack this tuft completely, or it may be reduced to a very few pinfeathers or small feathers.     

Hartnup disease. Clinical, pathological, and biochemical observations

Hartnup disease is a rare genetic disorder of amino acid transport associated with variable and intermittent clinical abnormalities. A family is described in which three siblings had an intermittently progressive neurological disease and two of the affected siblings had the Hartnup-pattern aminoaciduria. Neuropathological examination of one case showed severe diffuse atrophy, generalized neuronal loss in the cortex, and Purkinje cell loss in the cerebellum. In vivo and in vitro studies of intestinal amino acid transport in the surviving sibling indicated a partial defect in the transport of several neutral amino acids (tryptophan, alanine, serine, and methionine) with normal transport of other neutral amino acids (threonine, phenylalanine, histidine, tyrosine, and isoleucine). Transport of glycine, proline, hydroxyproline, and the basic amino acids appeared normal.     

Mental symptoms in Parkinson''s disease during chronic treatment with levodopa

The influence of epidural block with bupivacaine (Marcaine-adrenalin) on fetal heart rate, uterine activity, and the frequency and intensity of contractions was studied in twenty-five nulliparae at term. Uterine activity was found to decrease during the first 30 minutes following epidural block. In the time interval 30 to 40 minutes after epidural block uterine activity increased again and attained the same level as during the last 10 minutes before analgesia. The frequency of uterine contractions did not decrease after the block. The lower levels of uterine contractility were due only to a lower amplitude of the contractions. The regularizing effect of epidural analgesia on incoordinate uterine action was noted. The recording of fetal heart rate in the time interval studied revealed no pathological findings. Mode of delivery, mean labour duration and Apgar scores after epidural block were comparable with earlier studies of a larger patient population. This study suggest that epidural analgesia does not induce any important changes in fetal heart rate but temporarily decreases uterine activity.     

Effects of acetylsalicylic acid, dipyridamole, and hydrocortisone on epinephrine-induced myocardial injury in dogs

A reproducible model for producing diffuse myocardial injury (epinephrine infusion) has been developed to study the cardioprotective effects of agents or maneuvers which might alter the evolution of acute myocardial infarction. Infusions of epinephrine (4 mug per kilogram per minute for 6 hours) increased radiocalcium uptakes into intact myocardium and each of its subcellular components with the mitochondrial fraction showing the most consistent changes when compared to saline-infused control animals (4,957 vs. 827 counts per minute per gram of dried tissue or fraction). Myocardial concentrations of calcium also increased significantly (12.0 vs. 5.0 mg.per 100 Gm. of fat-free dry weight). Infusions of calcium chloride sufficient to raise serum calcium concentrations 2 mEq. per liter failed to increase calcium influx into the myocardial cell. Mitochondrial radiocalcium uptakes were significantly decreased in animals pretreated with acetylsalicylic acid or dipyridamole or when hydrocortisone was added to the epinephrine infusion (2,682,2,803, and 3,424 counts per minute per gram of dried fraction, respectively). Myocardial calcium concentrations also were decreased (11.2, 8.3, and 8.9 mg. per 100 Gm. of fat-free dry weight, respectively) in the three treatment groups, being significantly decreased only in the last two. Evidence of microscopic damage was graded as less severe in the three treatment groups. Acetylsalicylic acid, dipyridamole, and hydrocortisone all appear to have cardioprotective effects when tested in this model.     

Professional drivers: protection needed for a high-risk occupation

"On the job" motor vehicle deaths number more than 4,000 annually in the U.S. and comprise nearly one-third of all work-related deaths. Yet the Department of Labor has set no standards relating to on-the-road safety of the millions of workers whose jobs entail large amounts of driving, and Department of Transportation standards affecting occupational safety cover only drivers in interstate commerce. Drivers of some commercial vehicles, such as heavy trucks, are at special risk of injury because trucks have usually been exempted for many years from federal motor vehicle safety standards--such as standards for brakes and seatbelts--designed to prevent crashes or protect occupants in crashes. Observations based on a series of 150 fatal crashes involving tractor trailers illustrate the need for better protection of this large population of high-risk workers. Clarification of responsibility within the various federal agencies and application of available knowledge and technology are essential.