Lower Threshold Level Research Articles

Accurate assessment of sensitivity and optimum threshold for semiconductor laser preamplified optical receivers

A recently developed moment generating function (MGF) characterisation for a laser preamplified optical receiver is employed to effect rigorous performance assessment in terms of sensitivity and decision threshold setting. A modified Chernoff bound (MCB) is used as the basis for error probability estimation and a comparison with the simple Gaussian approximation (GA) is effected. The GA is shown to predict accurately receiver sensitivity but to indicate inappropriately low decision threshold levels when signal-dependent noise is significant.

Studies of limiting factors governing the waterflow requirement for Atlantic salmon ( Salmo salar L.) in landbased seawater systems

In the first part of the investigation two different models are derived to obtain the direct ratio between (a) total ammonia and oxygen and (b) unionized ammonia and oxygen as limiting factors for the waterflow requirement for salmonids in landbased seawater systems. In both models the mass related ammonia quotient, expressed as the ratio between total ammonia excreted (mg NH 4N per kilogramme fish per minute) and oxygen consumed (mg O 2 per kilogramme fish per minute) is an important factor. The second part of the study reports measurements of the mass related ammonia quotient (diurnal cycles) of Atlantic salmon kept in a landbased tank farm and calculations of waterflow requirements. The total variation find of the mass related ammonia quotient values were between 0·03 and 0·08. Based on two of the most extreme diurnal cycles with respect to temperature and fish size, the specific waterflow requirement applying ammonia as a limiting factor was in the range 0·04–0·17 litres/kg min. The third part of the study applies the measurements obtained for the ammonia quotient to the models. The results show that un-ionized ammonia may become the first limiting factor by combinations of a high difference in the dissolved oxygen concentration between the inlet water and the discharge, a high pH and a low threshold level for un-ionized ammonia. However, oxygen is usually found to be the first limiting factor when compared to un-ionized ammonia. If the value 0·5 mg NH 4N/litre is used as the limiting criterion for total ammonia, the difference in the dissolved oxygen concentration between the inlet water and the discharge should not exceed about 7 mg/litre. However, in seawater oxygenation is necessary to provide and maintain this difference. Therefore both models result in the same conclusion for moderate levels of oxygen addition.

Measurement of airborne mite antigen in homes of asthmatic children

The airborne concentration of major house dust mite antigen Der p1 was measured by low volume sampling (2 litres/min) in the homes of 68 allergic, asthmatic children. The presence of detectable airborne antigen was strongly associated with sensitivity to the mite, whereas there was no significant relation between sensitivity and the previously recommended threshold level of 2 μg Der p1 per g carpet dust. There was a significant association with lower threshold levels in carpet dust (0·5 μg/g) but at no level was the association as strong as that with air measurements. Concentrations of airborne antigen were higher in rooms with wool carpets than in those with synthetic carpets or hard floors, but there was no significant difference between the dust levels of Der p1 in the two carpet types. Air sampling is a more appropriate method of assessing antigen exposure than dust sampling for asthmatic patients.

Low levels of herpes simplex virus thymidine-thymidylate kinase are not limiting for sensitivity to certain antiviral drugs or for latency in a mouse model

Herpes simplex virus mutant KG111 contains a nonsense mutation at codon 44 of the viral thymidine kinase (tk) gene and produces low amounts of a truncated tk polypeptide. We tested mutant KG111 and related viruses that specify varying amounts of similar truncated tk polypeptides for their sensitivities to antiviral nucleoside analogs at different temperatures using plaque reduction assays. The results of these assays showed that the nonsense mutation confers high resistance to bromovinyldeoxyuridine (BVdU) at any temperature and temperature-dependent resistance to acyclovir (ACV), buciclovir (BCV), ganciclovir (DHPG), and fluoroiodoarabinouracil (FIAU). Above relatively low threshold levels of tk that varied depending on the drug tested, viruses exhibited full sensitivity to ACV, BCV, DHPG, and FIAU at 34 degrees. Below these threshold levels, however, decreases in drug sensitivity were linear with decreases in tk levels, forming the basis of a pharmacological assay for tk gene expression. Studies of thymidine (TdR) anabolism in infected 143 tk-cells showed that when high TdR concentrations were added to the medium, KG111 directed thymidine monophosphate (TMP) formation at rates consonant with the amount of tk polypeptide produced by the mutant. When low concentrations to TdR were added to the medium, however, KG111 directed TMP formation at a rate similar to that directed by wild-type virus, indicating that the truncation of the tk polypeptide had little or no effect on tk activity at 34 degrees. Subsequent anabolism to thymidine diphosphate and thymidine triphosphate was reduced in KG111-infected cells, indicating a defect in TMP kinase activity that explains this mutant's resistance to BVdU. Despite the low levels of tk and TMP kinase activity expressed by KG111, this mutant established reactivatable latent infections as efficiently as wild-type virus in a mouse model.

Optimization of water for fruit trees by a computerized irrigation system

irrigation according to programmable threshold soil matric potential (SMP) levels. The SMP control determined the water content and the irrigated soil volume and possibly the size of the active root system. This method enabled water to be supplied at the rate of consumptive use of the trees, and should eliminate water and mineral percolation to soil layers below the active root zone. During 3 consecutive years treatments consisting of high and low SMP threshold levels and a common commercial irrigation regime according to pan evaporation coefficients were applied. The control of SMP may stimulate root production in a limited volume of soil and thereby induce physiological root restriction effects such as reduction of vegetative to reproductive growth ratio. The main result obtained was a decrease in vegetative growth without impairing crop load (the ratio of reproductive to vegetative growth - kg fruit/cm2 trunk growth) and fruit size in the low SMP treatment irrigated with 213 mm less water than the treatment according to pan evaporation. It was concluded that this system of irrigation may reduce the size of the trees, and thereby increase light penetration, improve fruit quality, and lower the cost of production. This method will permit the planting of economically successful high density orchards.

Kinetics of propylene glycol elimination and metabolism in rat

The kinetics of 1,2-propanediol (PD) metabolism in vivo have been determined by employing the Michaelis-Menten rate equation; it was found that maximum metabolizing capacity was 8.33 mmole PD/kg/hr in the rat, which is equivalent to 1.06 kg/day for an average 70-kg human. The rate equation could be suitably used for optimizing the dosage schedule of a drug from the linear elimination pattern; in the present case this gave a K m value of 17.86 mmole/kg on the basis of the elimination rate of PD. The competitive inhibition of PD elimination by preadministration of pyrazole ( K i = 44 μmole/kg) demonstrated that the first step of the biotransformation of PD catalyzed by the NAD-dependent dehydrogenase might be the rate-limiting step for its in vivo metabolism. The low threshold level of the compound and significant rate of metabolism suggested that the CNS toxicity reported in clinical studies might be due to some of its metabolites such as lactaldehyde and other oxo compounds. Thus, PD could not be considered as an inert and innocuous substance.

EFFECT OF CROP ROTATION AND FERTILIZATION ON THE QUANTITATIVE RELATIONSHIP BETWEEN SPRING WHEAT YIELD AND MOISTURE USE IN SOUTHWESTERN SASKATCHEWAN

The effects of crop rotation and fertilization on the quantitative relationship between spring wheat (Triticum aestivum L.) yields (y), available spring soil moisture (AvSpSM), and growing season precipitation (GSP) were determined from an experiment conducted on a loam soil in the Brown soil zone of southwestern Saskatchewan for the period 1967–1984. Moisture used (MU) was defined as[Formula: see text]and AvSpSM as volumetric moisture content at time of planting minus the lowest soil moisture measured at harvest. For discussion of moisture use characteristics GSP was defined as precipitation received from 1 May to 31 Aug.; for predictive equations GSP was more effective if GSP was taken as 1 May–31 July. When the 18-yr data were analyzed, the relation of y to MU was curvilinear. If data for 1 or 2 yr (1970 and 1983) with skewed distribution of GSP were omitted, the relationship between y (kg ha−1) and MU (mm) for well-fertilized fallow- and stubble-seeded wheat combined was[Formula: see text](where GSP = 1 May to 31 July). This equation performed well when it was used to estimate yields of fallow- and stubble-seeded wheat in 1985 and 1986. Stubble-seeded wheat required 68 mm of moisture to produce the first kilogram per hectare of grain; fallow-seeded wheat required about 46 mm. There was no effect of fertilizer on these lower threshold values, but the yield increase per millimetre of MU tended to be greater for the better fertilized rotations. The main difference in our y vs. MU relationships compared to those reported for the period 1925–1950 was that the lower threshold level of MU for grain production decreased from about 140 mm to the values cited above; this has resulted in substantially greater moisture use efficiency in recent years likely due to better, more timely crop management and the improved cereal varieties now used. When y was related to AvSpSM and GSP (1 May to 31 July) analyzed as separate variables, the relationship was only improved in terms of coefficient of determination (R2) value when a quadratic model was used. However, the latter did not predict the 1985 and 1986 yields as well as the y vs. MU relationship did. For fallow-seeded wheat, the relative effect of GSP on yield variability was about 5.4 times as great as that of AvSpSM; for stubble-seeded wheat it was only 1.5 times as great. GSP was equally important in affecting yields of wheat grown on fallow or stubble. The grain-filling period was confirmed as the most important for the occurrence of precipitation for both fallow- and stubble-seeded wheat, but precipitation at or near seeding time was almost as important for stubble-seeded wheat since this ensures the establishment of an adequate plant stand. Key words: Available moisture, growing season precipitation, timeliness of precipitation, regression analysis

Comparative study of sympathetic and parasympathetic firing in automatic nerves produced by stimulating different structures of the cat hypothalamus

It was discovered by making simultaneous recordings of evoked hypothalamic-parasympathetic and hypothalamic-sympathetic firing that sympathetic discharges in the splanchnic nerve and parasympathetic discharges in the pelvic nerve with minimum latency and lowest threshold level could be obtained by stimulating the posterolateral hypothalamus. It was also found that the focus of maximum neuronal activity produced by stimulating afferent visceral nerve fibers as well as the highest concentration of evoked efferent response in sympathetic and parasympathetic nerves were located in the same hypothalamic area. A working hypothesis was put forward that convergent polysensory hypothalamic neurons also act as divergent polyeffector constituents of the integrative system of the hypothalamovisceral reflex arc.

Recovery profile of single motoneurons after electrical stimuli in man

The H-reflex of 120 soleus motoneurons was recorded using fibre EMG. The recovery profile of these motoneurons was studied during monitoring surface H-reflex records in 28 adult subjects. The spectrum of motoneurons tested was homogenous with two extremes of neurons having different characteristics. A motoneuron population (forming about 69% of our sample) had a high threshold level for electrical stimuli, short recovery time, and short recovery fringe time (called type A). A second population of motoneurons (forming about 20–30% of our sample) had a low threshold level for electrical stimuli, long recovery fringe time (called type B). During an isometric muscle contraction every motoneuron showed an early shift in recovery time (i.e. each had a shorter recovery time) with shortened recovery fringe time. These changes were larger for motoneurons type B than motoneurons type A. With paired identical electrical stimuli of varying interstimulus intervals a motoneuron may fire in response to the conditioning and test stimuli giving an H 2, but not response to both stimuli. This occured for interstimulus intervals of 4–11 ms. A strong inhibition period was recorded with interstimulus intervals of 12–80 ms in which all motoneurons did not show any recovery. Most motoneurons recovered in orderly fashion between 80 and 300 ms of interstimulus interval, and this recovery coincided with the fast recovery recorded in surface H-reflex. All motoneurons were recovered by 3000 ms of interstimulus intervals. These findings emphasize the importance of eliciting the H-reflex every 3–5 s in H-reflex methodology in order to be assured that all excited motoneurons have been recovered.

Metallothionein genes MTa and MTb expressed under distinct quantitative and tissue-specific regulation in sea urchin embryos.

Sea urchin embryo metallothionein (MT) mRNAs MTa and MTb have distinct cDNA sequences and are transcripts of different genes of a multigene family. These MT mRNAs differ in size and in their 3'-untranslated sequences. They encode proteins that are unusual among MT isotypes in that the relative positions of their cysteine residues are partially out of register, suggesting potential differences in function. In pluteus larvae MTa mRNA is expressed abundantly and exclusively in the ectoderm, while MTb mRNA, which is restricted to the endomesoderm at a low endogenous level, can be induced to a high level by heavy metal ions (M2+). MT mRNA is present in the maternal reservoir of the egg and is predominantly (greater than 95%) MTa mRNA. Endogenous expression in the embryo, which is at a much higher level than in the egg, requires M2+ for gene transcription, is developmentally regulated, and is greater than 90% MTa mRNA. When induced by added M2+, however, MTa and MTb mRNAs accumulate to almost equal levels. The differences in the ratios of MTa/MTb expressed endogenously and inductively are not attributable to differences in the stabilities of these MT mRNAs, which were observed under conditions of M2+ depletion, or in their inducibilities, which were observed at moderate to high M2+ levels. We found, instead, that the MTa gene responds to M2+ at a lower threshold level than MTb, so that at very low M2+ concentrations the ratio of induced MTa/MTb mRNA is high and equivalent to the endogenous ratio. Thus, endogenous expression of the MTa gene is selectively enhanced in the ectoderm by determinants that are responsive at low M2+ threshold concentrations.

Metallothionein genes MTa and MTb expressed under distinct quantitative and tissue-specific regulation in sea urchin embryos.

Sea urchin embryo metallothionein (MT) mRNAs MTa and MTb have distinct cDNA sequences and are transcripts of different genes of a multigene family. These MT mRNAs differ in size and in their 3'-untranslated sequences. They encode proteins that are unusual among MT isotypes in that the relative positions of their cysteine residues are partially out of register, suggesting potential differences in function. In pluteus larvae MTa mRNA is expressed abundantly and exclusively in the ectoderm, while MTb mRNA, which is restricted to the endomesoderm at a low endogenous level, can be induced to a high level by heavy metal ions (M2+). MT mRNA is present in the maternal reservoir of the egg and is predominantly (greater than 95%) MTa mRNA. Endogenous expression in the embryo, which is at a much higher level than in the egg, requires M2+ for gene transcription, is developmentally regulated, and is greater than 90% MTa mRNA. When induced by added M2+, however, MTa and MTb mRNAs accumulate to almost equal levels. The differences in the ratios of MTa/MTb expressed endogenously and inductively are not attributable to differences in the stabilities of these MT mRNAs, which were observed under conditions of M2+ depletion, or in their inducibilities, which were observed at moderate to high M2+ levels. We found, instead, that the MTa gene responds to M2+ at a lower threshold level than MTb, so that at very low M2+ concentrations the ratio of induced MTa/MTb mRNA is high and equivalent to the endogenous ratio. Thus, endogenous expression of the MTa gene is selectively enhanced in the ectoderm by determinants that are responsive at low M2+ threshold concentrations.

Disruption of corticospinal plasticity by 6-hydroxydopamine as measured by intracortical microstimulation in rats

Intracortical microstimulation in normal, adult rats evoked low-threshold contralateral and high-threshold ipsilateral forelimb movements. In comparison, stimulation of the intact cortex in adult rats that sustained unilateral cortical lesions at birth evoked ipsilateral movements at abnormally low-threshold levels in addition to normal contralateral movements. Depletion of cortical and spinal cord noradrenaline levels by treatment with 6-hydroxydopamine prior to the placement of neonatal cortical lesions eliminated the low-threshold ipsilateral movements when tested at maturity. These findings suggest that the noradrenergic system may influence corticospinal plasticity.

Growth pattern of the sex ducts in foetal mouse hermaphrodites

In this report the morphology of the gonads and the growth of the Wolffian and Müllerian duct in foetal mouse true hermaphrodites (16 days p.c.) have been studied and compared to that of normal mice. The ducts from the hermaphrodites were placed in one of five groups according to the proportion of male and female characteristic of the gonad. When more than 85% of the gonadal tissue was masculine, the Wolffian ducts showed the same percentage of cells in mitosis (mitotic index, MI) as normal males. The MI of the Wolffian ducts was lower, but constant, if the gonad contained between 0 and 85% of testicular tissue. The number of Leydig cells in the gonads showed a linear relationship with the percentage of testicular tissue. Apparently, the MI of the Wolffian duct does not increase with increasing 'maleness' and with the number of Leydig cells. Four possibilities are put forward to explain the constant level of MI: (1) The Leydig cells of hermaphrodites may be deficient in producing testosterone. (2) The Leydig cells may produce testosterone at a normal rate but the epithelial cells of the Wolffian duct may not respond to increasing levels of testosterone by increasing their mitotic activity. (3) The presence of female gonadal tissue may directly or indirectly inhibit the mitotic activity of the epithelial cells of the Wolffian duct. (4) The epithelial cells of the Wolffian duct may respond to a low threshold level of testosterone, but maximal response is only triggered by a critical higher hormone level present only in group V. In hermaphrodites, the Wolffian duct attached to a gonad without testicular tissue and without Leydig cells, has a MI which is significantly to a gonad without testicular tissue and without Leydig cells, has a MI which is significantly higher than in normal females. It is suggested that circulating testosterone from the contralateral gonad is responsible for this high MI. In the Müllerian duct a mitotic index similar to that of the normal females was only found when the gonad contained from 0 to 15% of testicular tissue. If a gonad contained more than 15% of testicular tissue, the MI of the attached Müllerian duct was much lower equalizing that of normal males. No influence on the growth of the Müllerian duct could be observed from the contralateral gonad.

Temperature profiles of hyperactive children.

An examination of temperament characteristics of hyperactive and control subjects indicates that, early in their lives, hyperactive children were viewed as having extreme temperament patterns characteristic of children difficult to rear. Primary hyperactive children were characterized by low threshold level, difficulties in staying on schedule, adjusting slowly to changes and being very active, and not being persistent. Implications of the findings for child-rearing practices are discussed.

Sex pheromonal activity of (+)-trans-verbenyl acetate and related compounds to the american cockroach,Periplaneta americana L.

The sex pheromone mimic of the American cockroach, (+)-trans-verbenyl acetate, and 67 synthesized analogs were tested for sex pheromonal activity using males of the cockroach. Only three esters in addition to the original (+)-trans-verbenyl acetate exhibited activity. (+)-trans-Verbenyl propionate and (+)-verbanyl acetate in particular showed stronger activity than the original mimic. None of the other analogs caused a response at the 1-mg level. The lower threshold levels at which even the most active analogs showed activity (0.02 mg) were many orders of magnitude higher than that of the natural pheromone, periplanone-B (10(-8) mg). From the structure-activity relationships, important structural factors for sex pheromonal activity in the original mimic were discussed.

The influence of advanced periodontitis on the psychophysical threshold level of periodontal mechanoreceptors in man.

Two groups of volunteers were examined with regard to the threshold level of a maxillary incisor for axialIy applied forces. One group showed an advanced periodontilis around the examined tooth, while the other group presented no clinical periodontal pathology. The ascending method of limits was used to determine the psychophysical threshold level.The relationship between the threshold level and the force application rate appeared to be linear on a lin‐log and a log‐log display. Higher rates gave lower threshold levels. For equal rales, the threshold level of the periodontilis group was significantly higher than for the control group.The results indicate that the periodontal mechanoreceptors are sensitive to the rate of force application, whatever the periodontal condition. Advanced periodontitis. however, clearly impairs the tactile function of the tooth supporting tissues.

Clinical variations in headband tension and potential effects on audiometric thresholds

The calibration of a standard audiometric headset is dependent upon headband tension. Similarly the attenuation provided by this standard, supra-aural headset is dependent upon the headband tension, and headband tension may change observably during clinical use. This is especially pertinent when one considers that masking from background noise is a serious problem when hearing levels are measured at or near the low reference threshold levels specified in the American National Standards Specifications for Audiometers, ANSI S3.6-1969. In the present study the degree of headband tension change during clinical threshold audiometry has been measured empirically. In addition the effect of these tension changes upon the obtained pure-tone thresholds at several frequencies were determined. Significant differences in obtained thresholds contingent upon deterioration of headband tension were noted. Results of this experiment will be discussed by reference to modeling of the acoustic impedance characteristics of a simple, single-cavity audiometric headset.

Longitudinal study of hearing in children: baseline data concerning auditory thresholds, noise exposure, and biological factors.

Serial auditory thresholds are being recorded at six-month intervals from 224 children and youths aged 4--18 years. The data from the first year show girls have lower threshold levels than boys, especially from 12--17 years, and, in both sexes, those aged 12--17 years have lower thresholds than those aged 6--11 years. Median total noise exposure scores tend to be higher in boys than girls, especially after 10 years of age, but these scores are not significantly correlated with auditory thresholds levels. The incidence of exposure to events associated with noise increases markedly in teenage boys and is related to auditory threshold levels. There are no significant associations between auditory thresholds levels and responses to general health questions or attained stature, but there are associations with meatal abnormalities. There is suggestive evidence, particularly in girls, that rapid maturation is associated with lower threshold levels, especially at lower frequencies.

Department of Biological Sciences, University of Warwick, Coventry, CV47AL, England.

Summary Interferon induction by 11 temperature-sensitive (ts) mutants of the HR strain, and 38 ts mutants of the AR339 strain of Sindbis virus was investigated. All HR and AR339 mutants induced interferon at 30 °C. Induction by the mutants at the restrictive temperature (39 °C) was dependent on the time of incubation, and, in some instances, on the input multiplicity. At an input multiplicity of 5, and after an incubation time of 16 h at 39 °C, induction by the AR339 mutants was dependent on virus RNA synthesis. All HR mutants showing detectable RNA synthesis at 39 °C induced interferon, but of those showing undetectable RNA synthesis at 39 °C, three induced interferon and three did not. At 42 °C, RNA synthesis by the HR wild-type and all ts mutants was depressed, and only one mutant and the wild type induced interferon. Temperature shift experiments showed that interferon induction was dependent on an early virus function. It is postulated that interferon induction is dependent on a low threshold level of RNA synthesis occurring early in infection.

Host preferences and discrimination by the mosquitoes Aedes aegypti and Culex tarsali (Diptera: Culicidae).

An experimental cage with a revolving turntable is described which permits host preference studies to be conducted in the laboratory and which yields results agreeing with field studies. The size and composition of the test population can be controlled, and conditions standardized, providing advantages over field studies. Using this experimental cage and sticky type traps, it was shown that Aedes aegypti (L.) preferred mice to chicks regardless of the weight ratio, while Culex tarsalis Coquillett only preferred the chicks when their weight was 2× that of the mice, otherwise showing no preference. C. tarsalis was attracted to frogs, toads, and lizards, but preferred mice or chicks. A. aegypti was not attracted to cold-blooded animals. A freeze trapping technique for the collection of animal odors which enables nonchemical separation of odor from carbon dioxide is described. Using this technique, it was found that chick and mouse odor is attractive to both species of mosquitoes, but that live mice are preferred to mouse odor. Human odor from the forearm is as attractive to A. aegypti as baby chick odor. No attractive odor from frogs or lizards was found. The mosquitoes were unable to distinguish mouse odor from chick odor when present in equal amounts. With all other factors being equal, the mosquitoes preferred whichever odor was the most abundant. The addition of CO2 to mouse odor increased its attractiveness to A. aegypti . No preference was shown by A. aegypti for either mouse odor plus mouse amounts of CO2 or chick odor phis chick amounts of CO2. The carbon dioxide with the chick odor was released at a rate 2.5× faster than that with the mouse odor. For A. aegypti CO2 is attractive, but once a low threshold level of CO2 is reached the addition of more does not cause increased attraction.