We study the statistical properties of a gas of interacting bosons trapped in a box potential in two and three dimensions. Our primary focus is the characteristic temperature \(\tchar\), i.e. the ...temperature at which the fluctuations of the number of condensed atoms (or, in 2D, the number of motionless atoms) is maximal. Using the Fock State Sampling method, we show that \(\tchar\) increases due to interaction. In 3D, this temperature converges to the critical temperature in the thermodynamic limit. In 2D we show the general applicability of the method by obtaining a generalized dependence of the characteristic temperature on the interaction strength. Finally, we discuss the experimental conditions necessary for the verification of our theoretical predictions.
Adrenomedullin (ADM) release is enhanced in pheochromocytoma, chronic heart failure (HF), hypertension and renal diseases. This study was designed to test the hypothesis that ADM secretion increases ...also in response to acute stimuli, such as static effort and to compare plasma ADM response to this stimulus in patients with chronic HF and healthy persons. Eight male HF patients (II/III class NYHA) and eight healthy subjects (C) performed two 3-min bouts of static handgrip at 30% of maximal voluntary contraction, alternately with each hand without any break between the bouts. At the end of both exercise bouts and in 5 min of the recovery period, plasma ADM and catecholamines were determined. In addition, heart rate, blood pressure, and stroke volume (SV) were measured. The baseline plasma ADM and noradrenaline levels were higher, whilst plasma adrenaline and SV were lower in HF patients than in C group. The 1st exercise bout caused an increase in plasma ADM from 3.32 +/- 0.57 to 4.98 +/- 0.59 pmol l(-1) (p<0.01) in C and from 6.88 +/- 0.58 to 7.80 +/- 0.43 pmol x l(-1) (p<0.02) in HF patients. The 2nd exercise bout did not produce further elevation in plasma ADM and during recovery the hormone concentration declined to pre-exercise or lower values. There were no differences between groups in exercise-induced increases in plasma ADM. Plasma ADM correlated with SV (r = -0.419) and with noradrenaline concentrations (r = 0.427). It is concluded that static exercise causes the short-lasting increase in plasma ADM concentration which is similar in healthy subjects and in patients with mild heart failure.
Eight healthy male volunteers (aged 19.6+/-3.0 years) were submitted to the unloaded active (AE) and passive (PE) cycling exercise-tests performed on an adapted cycle ergometer at a pedalling rate of ...50 rpm. Intensity of active exercise was about 10% of VO2 max. In the PE exercise test the ergometer was moved electrically. During both tests the systolic time intervals (STI), stroke volume (SV), heart rate (HR), blood pressure (BP), oxygen uptake (VO2), rating of perceived exertion (RPE), electrical muscle activity (EMG), plasma adrenaline (A), noradrenaline (NE) and blood lactate (LA) concentrations were measured. Exercise induced changes in VO2, RPE and EMG were significantly higher during AE than PE. Shortening of the pre-ejection period (PEP) and diminishing of the PEP to ejection time (ET) ratio were similar in both types of exercise, whereas HR increased only during AE. A significant increase in cardiac output (p<0.01) resulted from increased SV (p<0.01) during PE and from increased HR (p <0.01) during AE. MAP increased only during PE and it was higher than at rest and during AE (p<0.01). Absence of changes in SV and MAP during AE may be considered as a secondary effect of the decrease in TPR. Plasma catecholamines did not increase above resting values in either type of exercise. Blood LA concentration increased during both PE and AE but it reached higher values (p<0.01) after the latter test. The present data suggest that the inotropic state depends on the mechanoreflexes originated in skeletal muscles. However, contribution of changes in preload to shortening of PEP can not be excluded.
1. Knowledge of the regulatory effects of the crop canopy on weed seed germination is necessary to understand fully the behaviour of weed seed banks during a crop cycle. It is well known that canopy ...presence interferes with seed germination through modifications to the light and thermal environment, but the changing effect of a growing canopy has not been assessed, thus precluding the identification of shading-intensity thresholds for triggering the different types of canopy-detection mechanisms in different seed populations. 2. Field experiments were performed with artificially modified thermal and light environments, using two types of seed banks (seeds buried or located at the soil surface). Conditions below a wheat canopy were modified to match light and thermal conditions prevailing on bare soil (i.e. soil without vegetation). 3. Most weed emergence patterns during the early stages of crop establishment were not modified by the thermal regime produced by the incipient canopy compared with a bare soil control. However, the reduction of the red : far-red ratio from the bare soil value of 1·2-0·9 below the wheat canopy reduced germination of some weed species located at the soil surface, and the effect could by reversed by far-red filters. 4. The weed Galinsoga parviflora developed two generations during the crop cycle. The modified light and thermal environments beneath an establishing wheat canopy was not sufficient to inhibit the germination of Galinsoga parviflora, even if seeds were located at the soil surface. Only for seeds of the second generation, dispersed from seeds of the first plant generation, was there sufficient modification of the photothermal environment below the wheat canopy to interfere with dormancy termination. 5. Synthesis and applications. Understanding seed responses to modifications in the photothermal environment below a crop canopy (e.g. wheat crop) should allow us to improve weed management strategies by manipulating crop canopy attributes. This could be achieved by modification of sowing date, crop density, spatial arrangement and genotype. For example, increasing the crop plant density would diminish the number of weeds emerging during the first phase of crop establishment. This strategy would be appropriate where weed seeds are predominantly located at the soil surface, typically found in a no-till cropping system.
The aim of this study was to find out how early the moderate training effects appear and to check the hypothesis that familiarization with exercise protocol may contribute to an early physiological ...responses to training in previously sedentary subjects.
Twelve male, sedentary volunteers (22.0+/-0.7 yrs) were submitted to 3 weeks of a bicycle ergometer training, consisting of 45 min of exercise (at 70% VO(2)max), 3-4 times a week. The subjects performed 4 incremental exercise tests until volitional exhaustion: 2 before training (C1 and C2), and then after 1 (T1) and 3 (T3) weeks of training. During exercise HR, VO(2), electrical activity (EMG) of rectus femoris, biceps femoris, soleus and trapezius muscles were recorded and blood samples were taken for blood lactate (LA) determination.
Already after 1 week of training HR decreased (p<0.05) with a further decline after 3 weeks the training (p<0.01). Maximal work load after 3 weeks of training increased to 277+/-10.4 W vs 250+/-9.5 W (p<0.05), VO(2)max achieved higher values than in C1 and C2 tests (p<0.05) and LA and EMG thresholds were elevated (p<0.05).
A decrease in the resting and submaximal heart rate is the earliest effect of increased physical activity. Familiarization to exercise protocol decreased EMG of biceps femoris and soleus muscles during exercise, but did not influence that of rectus femoris muscle the most engaged during cycling.
Dormancy is a common attribute of many weed seed populations and this usually hampers the task of predicting timing and extent of emergence of weeds. Both the number of established plants and the ...timing of emergence of a weed are strongly related to the dynamics of dormancy release of the seed population. In this paper, we discuss the different factors that affect dormancy in weed seed banks in soil, aiming to set a conceptual basis that will facilitate the construction of predictive models. From the long list of factors that are known to control dormancy under field conditions, we distinguish those that modify the dormancy level of the population (i.e. soil temperature and soil hydric conditions) from those that terminate dormancy or in other words, remove the ultimate constraints for seed germination once the degree of dormancy is sufficiently low (i.e. light, fluctuating temperatures, nitrate concentration). We also discuss the effect of agricultural practices on dormancy of weed seed populations, making reference to studies that have evinced clearly the factor(s) involved in determining a particular pattern of response. Overall, we stress the importance of clarifying, both qualitatively and quantitatively, the interaction between soil thermal and hydric conditions in the modification of the degree of dormancy of seed populations. Similarly, it is essential that we understand the extent to which such changes in dormancy comprise changes in sensitivity to factors that terminate dormancy.
The aim of this study was to follow up the electromyographic activity (EMG) of dynamically working muscles with simultaneous determinations of blood lactate and plasma catecholamine concentrations ...during progressive exercise. Twenty eight male soccer players aged 20.6 +/- 0.8 yrs performed incremental bicycle ergometer exercise test. The test consisted of 3-min stages exercise separated by 1-min rest intervals. Work load at each stage increased by 50 W until volitional exhaustion. The root mean square (rms)-EMG activity of the rectus femoris and soleus muscles were recorded continuously during exercise. Venous blood samples were taken after each exercise stage for determination of blood lactate (LA). Additionally in seven subjects adrenaline (A) and noradrenaline (NA) concentrations were determined. The EMG activity increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to thresholds of blood lactate and plasma catecholamine accumulation (LA-T, A-T, NA-T). Close correlations (P < 0.001) were found between blood LA concentration and EMG derived from rectus f. (r = 0.72) and soleus (r = 0.68) muscles. The mean threshold exercise intensities for m. rectus f. and m. soleus EMG (176 +/- 9 W and 172 +/- 9 W, respectively) did not differ significantly from lactate (164 +/- 7 W), noradrenaline (178 +/- 6 W) and adrenaline (180 +/- 5 W) thresholds, all of them detected by log-log transformation. The results indicate that threshold character of EMG changes in dynamically working muscles reflects to some extend the patterns of blood lactate and plasma catecholamine changes during incremental exercise.
A screening method was used to characterize seed thermal responses of prostrate knotweed and common purslane, two important weeds invading wheat in the humid Pampa. Through this method, it was ...possible to detect thermal conditions that induce or break dormancy in both species. In addition, we were able to quantify changes in dormancy level in seed populations as a function of time of burial after dispersal, through changes in width of the thermal range within which germination can occur. Plotting the overlap of this thermal range and observed soil temperature throughout the year allowed the prediction of the seedling emergence period. This prediction was in agreement with observed seedling emergence in the field for both species, during 2 consecutive yr. From the analysis carried out under laboratory conditions, it was also possible to estimate required thermal time for germination of the nondormant fraction of the population and the base temperature above which thermal time is accumulated. The results obtained from this study are the basis for the formulation of seed germination models that predict not only the occurrence of seedling emergence in the field, but also the dynamics of germination within those periods.
The muscle contents of high-energy phosphates and their derivatives ATP, ADP, AMP, creatine phosphate (CrP), and creatine, glycogen, some glycolytic intermediates, pyruvate, and lactate were compared ...in 11 dogs performing prolonged heavy exercise until exhaustion (at ambient temperature 20.0 +/- 1.0 degrees C) without and with trunk cooling using ice packs. Without cooling, dogs were able to run for 57 +/- 8 min, and their rectal (Tre) and muscle (Tm) temperatures increased to 41.8 +/- 0.2 and 43.0 +/- 0.2 degrees C, respectively. Compared with noncooling, duration of exercise with cooling was longer by approximately 45% while Tre and Tm at the time corresponding to the end of exercise without cooling were lower by 1.1 +/- 0.2 and 1.2 +/- 0.2 degrees C, respectively. The muscle contents of high-energy phosphates (ATP + CrP) decreased less, the rate of glycogen depletion was lower, and the increases in the contents of AMP, pyruvate, and lactate as well as in the muscle-to-blood lactate ratio were smaller. The muscle content of lactate was positively correlated with Tm. The data indicate that with higher body temperature equilibrium between high-energy phosphate breakdown and resynthesis was shifted to the lower values of ATP and CrP and glycolysis was accelerated. The results suggest that hyperthermia developing during prolonged muscular work exerts an adverse effect on muscle metabolism that may be relevant to limitation of endurance.
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