845 resultados para variable intensity
Resumo:
Growing economic globalisation (a means of market extension) may increase the economic vulnerability of firms in modern industries, especially those in which firms experience substantial economies of scale. The possibility is explored that globalisation activates competitive pressures that forces firms into a situation where their leverage (fixed costs relative to variable costs, or overhead cost relative to operating costs or capital intensity) rises substantially. Consequently, they become increasingly vulnerable to a sudden adverse change in economic conditions, such as a collapse in the demand for their industry’s product. This is explored for monopolistically competitive markets and also for oligopolistic markets of the type considered and modelled by Sweezy using kinked demand curves. In addition, globalisation is hypothesised to induce firms to become more uniformly efficient. While this has static efficiency advantages, this lack of heterogeneity in productive efficiency of firms can make for economic inefficiency in the adjustment of the industry to altered economic conditions. It is shown that lack of variation in the economic efficiency of firms can impede the speed of market adjustment to new equilibria and may destabilise market equilibria.
Resumo:
The quantum trajectories method is illustrated for the resonance fluorescence of a two-level atom driven by a multichromatic field. We discuss the method for the time evolution of the fluorescence intensity in the presence of bichromatic and trichromatic driving fields. We consider the special case wherein one multichromatic field component is strong and resonant with the atomic transition whereas the other components are much weaker and arbitrarily detuned from the atomic resonance. We find that the phase-dependent modulations of the Rabi oscillations, recently observed experimentally [Q. Wu, D. J. Gauthier, and T. W. Mossberg, Phys. Rev. A 49, R1519 (1994)] for the special case when the weaker component of a bichromatic driving field is detuned from the atomic resonance by the strong-field Rabi frequency, appear also for detunings close to the subharmonics of the Rabi frequency. Furthermore, we show that for the atom initially prepared in one of the dressed states of the strong field component the modulations are not sensitive to the phase. We extend the calculations to the case of a trichromatic driving field and find that apart from the modulations of the amplitude there is a modulation of the frequency of the Rabi oscillations. Moreover, the time evolution of the fluorescence intensity depends on the phase regardless of the initial conditions and a phase-dependent suppression of the Rabi oscillations can be observed when the sideband fields are tuned to the subharmonics of the strong-field Rabi frequency. [S1050-2947(98)03501-X].
Resumo:
Six men were studied during four 30-s all-out exercise bouts on an air-braked cycle ergometer. The first three exercise bouts were separated by 4 min of passive recovery; after the third bout, subjects rested for 4 min, exercised for 30 min at 30-35% peak O-2 consumption, and rested for a further 60 min before completing the fourth exercise bout. Peak power and total work were reduced (P < 0.05) during bout 3 [765 +/- 60 (SE) W; 15.8 +/- 1.0 kJ] compared with bout 1 (1,168 +/- 55 mT, 23.8 +/- 1.2 kJ), but no difference in exercise performance was observed between bouts 1 and 4 (1,094 +/- 64 W, 23.2 +/- 1.4 kJ). Before bout 3, muscle ATP, creatine phosphate (CP), glycogen, pH, and sarcoplasmic reticulum (SR) Ca2+ uptake were reduced, while muscle lactate and inosine 5'-monophosphate were increased. Muscle ATP and glycogen before bout 4 remained lower than values before bout I (P < 0.05), but there were no differences in muscle inosine 5'-monophosphate, lactate, pH, and SR Ca2+ uptake. Muscle CP levels before bout 4 had increased above resting levels. Consistent with the decline in muscle ATP were increases in hypoxanthine and inosine before bouts 3 and 4. The decline in exercise performance does not appear to be related to a reduction in muscle glycogen. Instead, it may be caused by reduced CP availability, increased H+ concentration, impairment in SR function, or some other fatigue-inducing agent.
Resumo:
We consider one source of decoherence for a single trapped ion due to intensity and phase fluctuations in the exciting laser pulses. For simplicity we assume that the stochastic processes involved are white noise processes, which enables us to give a simple master equation description of this source of decoherence. This master equation is averaged over the noise, and is sufficient to describe the results of experiments that probe the oscillations in the electronic populations as energy is exchanged between the internal and electronic motion. Our results are in good qualitative agreement with recent experiments and predict that the decoherence rate will depend on vibrational quantum number in different ways depending on which vibrational excitation sideband is used.
Resumo:
This study examined the effects of 26 days of oral creatine monohydrate (Cr) supplementation on near-maximal muscular strength, high-intensity bench press performance, and body composition. Eighteen male powerlifters with at least 2 years resistance training experience took part in this 28-day experiment. Pre and postmeasurements (Days 1 and 28) were taken of near-maximal muscular strength, body mass, and % body fat. There were two periods of supplementation Days 2 to 6 and Days 7 to 27. ANOVA and t-tests revealed that Cr supplementation significantly increased body mass and lean body mass with no changes in % body fat. Significant increases in 3-RM strength occurred in both groups, both absolute and relative to body mass; the increases were greater in the Cr group. The change in total repetitions also increased significantly with Cr supplementation both in absolute terms and relative to body mass, while no significant change was seen in the placebo (P) group. Creatine supplementation caused significant changes in the number of BP reps in Sets 1, 4, and 5. No changes occurred in the P group. It appears that 26 days of Cr supplementation significantly improves muscular strength and repeated near-maximal BP performance, and induces changes in body composition.
Resumo:
Familial partial epilepsy with variable foci (FPEVF) joins the recently recognized group of inherited partial epilepsies. We describe an Australian family with 10 individuals with partial seizures over four generations. Detailed electroclinical studies were performed on all affected and 17 clinically unaffected family members. The striking finding was that the clinical features of the seizures and interictal electroencephalographic foci differed among family members and included frontal, temporal, occipital, and centroparietal seizures. Mean age of seizure onset was 13 years (range, 0.75-43 years). Two individuals without seizures had epileptiform abnormalities on electroencephalographic studies. Penetrance of seizures was 62%. A genome-wide search failed to demonstrate definitive linkage, but a suggestion of linkage was found on chromosome 2q with a LOD score of 2.74 at recombination fraction of zero with the marker D2S133. FPEVF differs from the other inherited partial epilepsies where partial seizures in different family members are clinically similar. The inherited nature of this new syndrome may be overlooked because of relatively low penetrance and because of the variability in age at onset and electroclinical features between affected family members.
Resumo:
Modulated chlorophyll fluorescence techniques were used to examine the effects of cyanide (NaCN) from cyanide fishing on photosynthesis of the symbiotic algae (zooxanthellae) located within the tissues of the zooxanthellate hard coral Plesiastrea versipora. Incubating corals for 3 h in a cyanide concentration of >10(-5) M NaCN under a saturating light intensity (photosynthetically active radiation [PAR] intensity of 250 mu mol quanta m(-2) s(-1)) caused a long-term decrease in the ratio of variable to maximal fluorescence (dark-adapted F-v/F-m). The effect of cyanide on dark-adapted F-v/F-m was Light dependent; thus F-v/F-m only decreased in corals exposed to 10(-4) M NaCN for 3 h under PAR of 250 mu mol quanta m(-2) s(-1). In corals where dark-adapted F-v/F-m was significantly lowered by cyanide exposure, we observed significant loss of zooxanthellae from the tissues. causing the corals to discolour (bleach). To further examine the light-dependent effect of cyanide and its relation to loss of zooxanthellae, corals were exposed to 10-4 M NaCN or seawater only (control), either in darkness or under 250 mu mol quanta m(-2) s(-1). ill significant decrease in dark-adapted F-v/F-m and loss of zooxanthellae only occurred in corals exposed to cyanide in the light. These results suggest cyanide causes the dissociation of the symbiosis (bleaching) by affecting photosynthesis of the zooxanthellae. Quenching analysis using the saturation-pulse technique revealed the development of high levels of non-photochemical quenching in cyanide-exposed coral. This result is consistent with the known property of cyanide as an inhibitor of the dark reactions of the Calvin cycle, specifically as an inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Therefore, chronic photoinhibition and an impairment of photosynthesis of zooxanthellae provides an important 'signal' to examine the environmental effects of cyanide fishing during controlled releases in situ.
Resumo:
Preparation of a series of specific penta- and tetra-amine derivatives of Co-III and Cr-III with a neutral leaving ligand has been carried out in order to accomplish a fine tuning of the associativeness/dissociativeness of their substitution reactions. Spontaneous aquation reactions of the neutral ligands have been studied at variable temperature and pressure. Although rate constants and thermal activation parameters show an important degree of scatter, the values determined for the activation volumes of the substitution process illustrate the mechanistic fine tuning that may be achieved for these reactions. In all cases, in the absence of important steric constraints in the molecule, electronic inductive effects seem to be the most important factor accounting for the dissociative shifts observed both for pentaamine (i.e.Delta V double dagger=+4.0 or +14.0 cm(3) mol(-1) and +5.2 or +16.5 cm(3) mol(-1) for the aquation of cis- or trans-[Co(MeNH2)(NH3)(4)(DMF)](3+) and cis- or trans-[CoL15(DMF)](3+) respectively, where L-15 represents a pentaamine macrocyclic ligand), and tetraamine systems (i.e.Delta V double dagger=+4.1 or +8.4 cm(3) mol(-1) and -10.8 or -7.4 cm(3) mol(-1) for the aquation of cis-[Co(NH3)(4)Cl(DMAC)](2+) (DMAC=dimethylacetamide) or cis-[Co(en)(2)Cl(DMAC)](2+) and cis-[Cr(NH3)(4)Cl(DMF)](2+) or cis -[Cr(en)(2)Cl(DMF)](2+)). From the results, clear evidence is obtained which indicates that, only when the situation is borderline I-a/I-d, or the steric demands are increased dramatically, dissociative shifts are observed; in all other cases electronic inductive effects seem to be dominant for such a tuning of the substitution process.
Reflex activation on arousal from sleep: An investigation of factors that may modulate its intensity
Resumo:
This study examined the effects of four high-intensity interval-training (HIT) sessions performed over 2 weeks on peak volume of oxygen uptake (VO2peak), the first and second ventilatory thresholds (UT VT2) and peak power output (PPO) in highly trained cyclists. Fourteen highly trained male cyclists (VO2peak = 67.5 +/- 3.7 ml . kg(-1) . min(-1)) performed a ramped cycle test to determine VO2peak VT1 VT2, and PPO. Subjects were divided equally into a HIT group and a control group. The HIT group performed four HIT sessions (20 x 60 s at PPO, 120 s recovery); the V-02peak test was repeated <I wk after the HIT program. Control subjects maintained their regular training program and were reassessed under the same timeline. There was no change in V0(2peak) for either group; however, the HIT group showed a significantly greater increase in VT1, (+22% vs. -3%), VT2 (+15% vs. -1%), and PPO (+4.3 vs. -.4%) compared to controls (all P <.05). This study has demonstrated that HIT can improve VT1, VT2,, and PPO, following only four HIT sessions in already highly trained cyclists.
Resumo:
Two families, originally diagnosed as having nonsyndromic X-linked mental retardation (NSXLMR), were reviewed when it was shown that they had a 24-bp duplication (428-45 1dup(24bp)) in the ARX gene [Stromme et al., 2002: Nat Genet 30:441-445]. This same duplication had also been found in three other families: one with X-linked infantile spasms and hypsarrhythmia (X-linked West syndrome, MIM 308350) and two with XLMR and dystonic movements of the hands (Partington syndrome, MIM 309510). On review, manifestations of both West and Partington syndromes were found in some individuals from both families. In addition, it was found that one individual had autism and two had autistic behavior, one of whom had epilepsy. The degree of mental retardation ranged from mild to severe. A GCG trinucleotide expansion (GCG)10+7 and a deletion of 1,517 by in the ARX gene have also been found in association with the West syndrome, and a missense mutation (1058C >T) in a family with a newly recognized form of myoclonic epilepsy, severe mental retardation, and spastic paraplegia [Scheffer et al., 2002: Neurology, in press]. Evidently all these disorders are expressions of mutations in the same gene. It remains to be seen what proportions of patients with infantile spasms, focal dystonia, autism, epilepsy, and nonsyndromic mental retardation are accounted for by mutations in the ARX gene. (C) 2002 Wiley-Liss, Inc.
Resumo:
This paper addresses the investment decisions considering the presence of financial constraints of 373 large Brazilian firms from 1997 to 2004, using panel data. A Bayesian econometric model was used considering ridge regression for multicollinearity problems among the variables in the model. Prior distributions are assumed for the parameters, classifying the model into random or fixed effects. We used a Bayesian approach to estimate the parameters, considering normal and Student t distributions for the error and assumed that the initial values for the lagged dependent variable are not fixed, but generated by a random process. The recursive predictive density criterion was used for model comparisons. Twenty models were tested and the results indicated that multicollinearity does influence the value of the estimated parameters. Controlling for capital intensity, financial constraints are found to be more important for capital-intensive firms, probably due to their lower profitability indexes, higher fixed costs and higher degree of property diversification.
Resumo:
Managing a variable demand scenario is particularly challenging on services organizations because services companies usually have a major part of fixed costs. The article studies how a services organization manages its demand variability and its relation with the organization`s profitability. Moreover, the study searched for alternatives used to reduce the demand variability`s impact on the profitability of the company. The research was based on a case study with a Brazilian services provider on information technology business. The study suggests that alternatives like using outsourced employees to cover demand peaks may bring benefits only on short term, reducing the profitability of the company on long term: Some options are revealed, like the internationalization of employees and the investment on developing its own workforce.
Resumo:
Over 1000 marine and terrestrial pollen diagrams and Some hundreds of vertebrate faunal sequences have been studied in the Austral-Asian region bisected by the PEPII transect, from the Russian arctic extending south through east Asia, Indochina, southern Asia, insular Southeast Asia (Sunda), Melanesia, Australasia (Sahul) and the western south Pacific. The majority of these records are Holocene but sufficient data exist to allow the reconstruction of the changing biomes over at least the past 200,000 years. The PEPII transect is free of the effects of large northern ice caps yet exhibits vegetational change in glacial cycles of a similar scale to North America. Major processes that can be discerned are the response of tropical forests in both lowlands and uplands to glacial cycles, the expansion of humid vegetation at the Pleistocene-Holocene transition and the change in faunal and vegetational controls as humans occupy the region. There is evidence for major changes in the intensity of monsoon and El Nino-Southern oscillation variability both on glacial-interglacial and longer time scales with much of the region experiencing a long-term trend towards more variable and/or drier climatic conditions. Temperature variation is most marked in high latitudes and high altitudes with precipitation providing the major climate control in lower latitude, lowland areas. At least some boundary shifts may be the response of vegetation to changing CO2 levels in the atmosphere. Numerous questions of detail remain, however, and current resolution is too coarse to examine the degree of synchroneity of millennial scale change along the transect. (C) 2003 Elsevier Ltd and INQUA. All rights reserved.