Structure--activity relationships in cephalosporins prepared from penicillins. 1. 7beta-Acylamino derivatives of 3-benzyl- and 3-(3-pyridylmethyl)ceph-3-em-4-carboxylic acids

tert-Butyl 7beta-aminoceph-3-em-4-carboxylates carrying either benzyl or 3-pyridylmethyl substituents at position 3 have been prepared by a multistep modification of the penicillin nucleus. Acylation of either amine, followed by deprotection, gave a range of new cephalosporins. The relationship between structure and antibacterial activity is discussed. D-Phenylglycine proved to be a preferred side chain in both series.     

Measuring the quantum correction at zero bias in metal-oxide-metal diode noise

According to van der Ziel's interpretation of Tucker's calculation of the noise and admittance of metal-oxide-metal (MOM) diodes, these devices, when operating at high frequencies (100 GHz) and low temperatures (2 K), show a transition from quantum thermal noise at zero bias to shot noise at ±1 mV bias. By slowly modulating the bias of the MOM diode between -1 mV and +1 mV, mixing and amplifying the noise, passing it through a quadratic detector and then LF filtering the detected MOM noise power, one can display the MOM diode noise power on a cathode ray oscillograph or strip-chart recorder as a function of bias, and thus calibrate the thermal noise at zero bias against the shot noise at higher bias.     

Place navigation by rats in a swimming pool.

Describes characteristics of place navigation by rats in the Morris water task. Ss learned to find a small invisible platform in a large, circular swimming pool to escape from cool milk. A variety of spatial localization strategies, including spatial mapping, response sequencing, and distal cue navigational strategies, were demonstrated. Using variants of this task, the following was demonstrated: (a) Rats very readily learned true mapping strategies, being able to swim directly to the invisible platform from anywhere in the pool after only a few trials; this ability was not dependent on navigating by specific distal cues nor on starting from a familiar place. (b) Ss acquired information that facilitated subsequent place navigation merely by viewing the room from the location of the invisible goal. (c) The location of the invisible platform was remembered extremely well for several weeks. (d) The availability of only distal auditory beacons permitted acquisition of an accurate spatial mapping strategy. (e) A single S could acquire both mapping and nonmapping strategies in the swimming pool and apply them when required by the situation. Results emphasize the utility of the Morris water task and demonstrate some of the basic features of mapping and nonmapping strategies in solving a variety of spatial problems. (French abstract) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of hot spots on the noise characteristic of large-area bipolar transistors

Measurements indicate that when hot spots are formed in large-area silicon power transistors, the $\text{1}\text{f}$ noise increases and a new noise component with a $\text{1}\text{f}{}^2$ spectrum shows up. The increase in $\text{1}\text{f}$ noise is attributed to the decrease in effective device area when the hot spot is formed. The noise with a $\text{1}\text{f}{}^2$ spectrum is attributed to a thermal feedback effect in the hot spot.     

The variation of integrated backscatter in human hearts in differing ultrasonic transthoracic views

It has been shown previously that in normal subjects the interventricular septum imaged in the long-axis view (LAX) and the left ventricular posterior wall imaged in both the LAX and the short-axis view (SAX) exhibit cyclic variation of integrated backscatter (IB) throughout the cardiac cycle, with maximum values occurring at end diastole (ED) and minimum at end systole (ES). The ability to demonstrate this cyclic variation within these myocardial regions in only two ultrasonic views has limited the potential clinical utility of an IB imaging system. To determine whether clinically useful information on the variation of IB is available from different myocardial regions in different ultrasonic views, we measured ED to ES variation of IB from the parasternal and apical views in normal subjects with a radiofrequency acquisition technique. Two independent clinical observers analyzed ED to ES variation of IB from 14 normal volunteers (mean age 32 +/- 6 years; range 21 to 45 years) in reconstructed two-dimensional ultrasonic images obtained from the parasternal LAX and SAX and apical two-chamber (2C) and four-chamber (4C) views. ED to ES variation of IB was measured from manually traced regions of interest (ROI) within the myocardium. These ROIs were chosen interactively and were located within the midposterior wall and the midanteroseptum in LAX views; within the midposterior wall, midanteroseptum, midseptum, and midlateral wall in SAX views; within the midseptum and the midlateral wall in 4C views; and within the midinferior wall and the midanterior wall 2C views. In all analyzed ROIs within the parasternal and apical views, ED to ES variation of IB was found. We have shown that the maximum magnitude of IB was at ES within the midseptum and in 10 out of 14 volunteers in the midanteroseptum measured from SAX views, the midanterior wall from 2C views, and the midlateral wall from 4C views. The rest of the ROIs analyzed exhibited the maximum value of IB cyclic variation at ED. We have confirmed that the ED to ES variation of IB is present not only when measured from the two standard parasternal views but also from the two apical views in all analyzed myocardial walls, and the minimum of this cyclic variation was not always coincident with ES nor the maximum with ED.     

The influence of boron induced and oxidation induced defects on bipolar transistor slice yield

Silicon lattice defects induced by high concentration boron diffusion, or by oxidation, are a major cause of high leakage currents in bipolar transistors. The incidence of such defects in narrow base, high frequency, transistors is investigated using Sirtl etch and the transmission electron microscope, and related to the transistor leakage currents. Boron induced defects are found to cause high emitter-base leakage, but it is shown that their density may be reduced by a nitric acid boron glass strip prior to base drive. A particular type of oxidation induced defect is found to cause high collector-emitter leakage, and appearance of this defect is correlated with silicon material batch. As an example, yields of slices of the British Telecom 40 Type submarine cable transistor meeting a specification including low leakage currents, are shown to be related closely to the silicon material/boron glass strip combination used.     

Algal and invertebrate communities in three subarctic lakes receiving mine wastes

The effects of liquid mine wastes on the density, species composition and diversity of phytoplankton and zooplankton were determined between May 1977 and May 1978 in a series of three small, shallow lakes (Meg, Keg, Peg Lakes), situated in the Canadian subarctic. The concentrations of the most common toxicants fluctuated widely during the study in each of the lakes. Meg Lake was the most polluted, with the concentrations of arsenic, lead, cyanide and copper reaching 3.0, 0.65, 0.60 and 0.65 g m⁻³ respectively. Although the levels of arsenic and lead in the other two lakes were roughly similar to those recorded in Meg Lake, cyanide and copper usually fell below detectable limits. Overall, changes in the level of contamination were poorly correlated with variations in the abundance of the flora and fauna. While phytoplankton (Chlamydomonas lapponica, Aphanothece microspora) were common in Meg Lake, reaching densities of 200 mg m⁻³, zooplankton were either rare or absent. Algal populations in Keg and Peg Lakes, which were dominated by Chlamydomonas lapponica and Oocystis parva, attained maximum densities of 200 and 150 mg m⁻³ respectively. The most common zooplankter, Keratella quadrata, maintained populations of up to 20–40 × 10⁺ animals m⁻³, and was followed in abundance by Daphnia middendorfiana and Cyclops bicuspidatus thomasi. It is concluded that: (1) The prevalent species may have developed a resistance to metals, (2) taxa not previously associated with heavy metal contamination may have the ability to adapt to pollution, and (3) high arsenic and lead levels probably had less impact on zooplankton than on phytoplankton, under field conditions.     

Cholinergic receptor blockade impairs spatial localization by use of distal cues in the rat.

Studied spatial localization in the Morris water maze. 30 male Long-Evans hooded rats were required to escape from cool water by finding a submerged, invisible platform located at a fixed place. The start point randomly varied, and there were no local cues. After training, the platform was moved. Six Ss subjected to central cholinergic receptor blockade with atropine sulfate were compared with normal Ss and with 6 Ss receiving peripheral cholinergic blockade with atropine methylnitrate. The controls were a group of blind Ss and Ss for which the platform was moved from trial to trial. Results show that controls and the atropine methylnitrate Ss used a spatial mapping strategy to locate the platform. The atropine sulfate-treated Ss adopted a search strategy like that of the blind Ss and Ss for which the platform was randomly moved. Results support the idea that central cholinergic systems are important for spatial mapping, which demands the use of distal visual cues. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)