The acoustic reflex at low sensation levels

The acoustic stapedial reflex, which normally occurs at a hearing level of about 80 dB, can be detected at lower levels by means of preactivation. Two techniques are presented, which allow the detection of reflex activity at intensities from 30 to 50 dB HL. It was the authors' intention to find a way to determine the hearing threshold from the stapedius reflex threshold even in patients, in whom the hearing threshold was not horizontal.     

高速钢粉末低压热压的研究

采用计算机测控法研究了高速钢粉末低压热压过程中的致密化现象, 随着热压温度由1 215 ℃升高至1 238℃时, 有效屈服应力由3~4 MPa降至2~3 MPa以下。在1 220~1 230 ℃和4.5 MPa压力下制备了Mo系高速钢剃齿刀, 相对密度达到99.85%, 碳化物的粒度为3~7μm。与普通高速钢刀具相比, 低压热压法制备的M4粉末高速钢剃齿刀寿命明显提高, 减少残余孔隙度对改善刀具的疲劳寿命是很重要的。充分利用材料在高温下, 特别是在接近固相线温度时屈服现象, 可以实现在低压下的粉末材料致密化, 其压力比热等静压低一个数量级, 这可能是一条较为经济的技术途径。     

On the reactions 2 C + O2 and C + CO2 at very low pressure

In an ultra high vacuum heterogeneous gas reactions such as 2 C + O₂^G → 2 CO^G and C + CO₂^G → 2 CO^G often show a less complicated reaction path than under normal pressure. In the present study the graphite sample is a commercial light‐bulb filament, which is extremely resistant against oxidation. Under low pressure the combustion reaction is of first order with a continuous transition to zero order at temperatures between 900 and 1300 K depending on the oxygen pressure. The Boudouard reaction behaves similarly but obeys zero order only around 2000 K and for CO₂ pressures around 1 bar. The measured and the statistically calculated reaction rates agree well. An insight of the details of the reaction and chemisorption is determined by the evaluation of experiments carried out in an ultra high vacuum using isotopes such as ¹³CO₂^G. The Boudouard equilibrium for graphite can be reached only catalytically, e.g., with sponge iron in statu nascendi.     

Good growth despite very low levels of insulin-like growth factors

1. The antioxidant thioctic acid (TA) has been used in the treatment of diabetic neuropathy and recent studies have suggested that TA also has pancreatic and peripheral effects that improve glucose transport and metabolism. In the present study, the metabolic effects of TA were evaluated in rodent models of insulin resistance (fructose-fed Sprague-Dawley rat) and insulin deficiency (streptozotocin (STZ)-induced diabetic rat). Oral and intravenous glucose tolerance tests (OGTT and IVGTT, respectively) were performed in conscious rats after treatment with 50 mg/kg per day TA or vehicle for 5 days. 2. Fructose feeding for 7 days induced insulin resistance and impaired glucose tolerance and hypertriglycerideaemia. Treatment of fructose-fed rats with TA had no significant effect on fasting or stimulated glucose levels or on fasting triglyceride concentrations (e.g. the area under the curve for glucose (AUCglu) following OGTT was 1233 +/- 67 and 1284 +/- 59 in fructose-fed rats treated with either TA (n = 12) or vehicle (n = 12), respectively). Similarly, TA had no significant effect on IVGTT profiles in fructose-induced insulin resistance. 3. Low-dose STZ (80 mg/kg, i.p., over 2 days) induced hyperglycaemia, but TA had no significant glucose-lowering effects in STZ-diabetic rats (AUCglu (OGTT) following oral administration was 5507 +/- 27 and 5450 +/- 27 in TA (n = 12) and vehicle-treated (n = 12) rats, respectively). Nor did pretreatment with TA affect the diabetogenic response to STZ. 4. In contrast with previous in vitro studies reporting favourable metabolic effects of TA, the present study shows that after short-term oral therapy there are no significant improvements in glucose tolerance in rodent models of insulin resistance and insulin deficiency. Thioctic acid is unlikely to be of therapeutic benefit as an anti-diabetic drug in clinical practice.     

The role of impurities during creep and superplasticity at very low stresses

It is well documented that impurities play an important role in the deformation and fracture of polycrystalline materials. For example, the results of a number of studies have demonstrated that the presence of a very small of amount of impurities in polycrystalline materials can explain many phenomena such as temper embrittlement in steels, creep embrittlement, and enhancement of ductility in the intermetallic compound Ni₃Al. This article reviews the details of two high-temperature deformation phenomena whose characteristics are, according to very recent experimental evidence, influenced or controlled by impurities. The first phenomenon, micrograin superplasticity, deals with the ability of fine-grained materials (d<10 μm, where d is the grain size) to exhibit extensive neck-free elongations during deformation at elevated temperatures above 0.5 T _m, where T _m is the melting point. The second phenomenon, Harper-Dom creep, refers to the anomalous creep behavior of large-grained materials at very low stresses and temperatures near the melting point. It is shown that while these two phenomena are different in terms of the conditions of occurrence and the characteristics of deformation, they share three common features: (1) stresses applied to produce deformation are very small; (2) impurities control the deformation characteristics such as the shape of the creep curve, the value of the stress exponent, and the details of the substructure; and (3) boundaries play a key role during deformation. This article is based on a presentation made in the workshop entitled “Mechanisms of Elevated Temperature Plasticity and Fracture,” which was held June 27–29, 2001, in San Diego, CA, concurrent with the 2001 Joint Applied Mechanics and Materials Summer Conference. The workshop was sponsored by Basic Energy Sciences of the United States Department of Energy.     

Intrinsic compressibility and volume compression in solvated proteins by molecular dynamics simulation at high pressure

Constant pressure and temperature molecular dynamics techniques have been employed to investigate the changes in structure and volumes of two globular proteins, superoxide dismutase and lysozyme, under pressure. Compression (the relative changes in the proteins' volumes), computed with the Voronoi technique, is closely related with the so-called protein intrinsic compressibility, estimated by sound velocity measurements. In particular, compression computed with Voronoi volumes predicts, in agreement with experimental estimates, a negative bound water contribution to the apparent protein compression. While the use of van der Waals and molecular volumes underestimates the intrinsic compressibilities of proteins, Voronoi volumes produce results closer to experimental estimates. Remarkably, for two globular proteins of very different secondary structures, we compute identical (within statistical error) protein intrinsic compressions, as predicted by recent experimental studies. Changes in the protein interatomic distances under compression are also investigated. It is found that, on average, short distances compress less than longer ones. This nonuniform contraction underlines the peculiar nature of the structural changes due to pressure in contrast with temperature effects, which instead produce spatially uniform changes in proteins. The structural effects observed in the simulations at high pressure can explain protein compressibility measurements carried out by fluorimetric and hole burning techniques. Finally, the calculation of the proteins static structure factor shows significant shifts in the peaks at short wavenumber as pressure changes. These effects might provide an alternative way to obtain information concerning compressibilities of selected protein regions.     

The retraction pressure during neurosurgical operations on the brain. III. An analysis of the efficacy of prophylactic methods aimed at reducing brain volume

The comparison was undertaken to examine 31 patients with various brain neurosurgical abnormalities to evaluate the efficiency of some of the most widely used preventive measures for retraction ischemia, which are aimed at reducing the brain volume at surgery: preoperative administration of a saluretic, osmodiuretic solution, hyperventilation, tumor cyst puncture, lumbar and ventricular drainage. The findings suggest the efficacy of such approaches, as tumor cyst puncture, intravenous administration of an osmodiuretic, ventricular and, possibly, lumbar drainage. Such methods as preadministration of saluretic hyperventilation are ineffective.     

Feasibility for evaluation of the efficacy of conventional ventilatory support in very low birth weight infants

Morbidity and mortality analysis in prematurely born low birth weight (LBW) neonates, very low birth weight (VLBW) neonates and extremely low birth weight (ELBW) neonates forms the cornerstone in current pediatric decision-making from both medical and socioeconomic point of view. The successful introduction of artificial ventilation for neonatal respiratory failure treatment has changed tremendously the prognosis of many diseases with a fatal outcome. This retrospective observational longitudinal study was designed to evaluate the changes in the following main indices: mean airway pressure (MAP), oxygenation index (OI), arterial-to-alveolar oxygen tension ratio (a/A PO2), alveolar-arterial oxygen gradient (A-a)DO2, ventilation index and VEI in VLBW infants treated with conventional ventilatory support (CV), assess the information yield of these indices as indicators of gas exchange at each and every one moment of CV, and to analyze their feasibility, accuracy and real-time convenience as indicators of the adequacy of inhalation therapy and their role as an indispensable tool in constructing the optimal treatment regimen in VLBW infants. Forty-seven VLBW infants requiring ventilatory support within 24 hours of birth were enrolled in the study. Four of the infants survived and the remaining 43 died. The data collected were entered into a high-yield Neonatal Intensive Computer File and the indices were followed up sequentially and thoroughly analyzed as the primary outcome measures of the study. Our results show that: 1. The combination of indices we propose is a useful high-yield discriminating method for evaluating the efficacy of neonatal ventilatory support, arterial blood gas exchange and clinical status. 2. These indices allow early diagnosis of the changes in pulmonary mechanics, hemodynamics and blood saturation. 3. Using the combination of indices improves the diagnostic reliability and information yield of each one of them. 4. The twofold pattern of change of the indices in VLBW infants is well-recognized:--whereas a/A and OI change rapidly in the group of non-survivors reflecting the delicate balance in optimal gas-exchange using conventional methods in the survivors group there is a sustained tendency towards an increase in a/A values with a concomitant decrease in OI values. The airway pressure is constant in the presence of great fluctuations in OI values reflecting the breakdown in oxygenation at the high price paid for its sustenance in the nonsurvivors group whereas the mean airway pressure showed a gradual decrease in the survivors group and allowed early weaning from mechanical ventilation. (A-a)DO2 remained high in the non-survivors group thus reflecting a high-degree, practically constant shunting whereas the same index showed a tendency towards decrease in the survivors group. 5. These indices allow optimal management of neonatal ventilation and oxygenation and timely correction or a change of the ventilatory or/and oxygenation strategy. 6. This information forms the basis for prognostic conclusions regarding the current status or the survival of the neonates.     

The effects of original and randomized rapseed oils containing high or very low levels of erucic acid on cardiac lipids and myocardial lesions in rats

The nutritional status of the very lowerucate, rapseed oil, Brassica napus var. 'Tower,' was compared with that of the high-erucate oil, Brassica napus var. 'Target,' as well as with corn oil. The effect of randomization on the nutritional qualities of rapeseed oil was investigated as well. The feeding of diets containing the original and randomized 'Tower' oil or the original 'Target' oil, at the 20% level by weight, gave growth rates which were not significantly different from that for corn oil. However, the randomized 'Target' oil gave growth rates which were significantly less than all other groups. The growth results could not be explained simply on the basis of food consumption. The level of triglycerides in the hearts of rats fed the very low-erucate oils was not significantly different from the corn oil group. Triglyceride concentrations in the hearts of animals given the high-erucate oils were 7-12 times greater than all other groups. The level of total fatty acids in tissue phospholipids was the same regardless of dietary treatment. Fatty acid compositions of the tissue lipid were the same in animals fed either the original or randomized rapeseed oils. A much higher incidence of focal myocardial necrosis was found in animals receiving high-erucate rapeseed oil relative to animals given the corn oil. The incidence in rats fed diets containing very low-erucate rapeseed oil was intermediate between these latter two extremes.