Strings in Cosmological and Black Hole Backgrounds: Ring Solutions

The string equations of motion and constraints are solved for a ring shaped Ansatz in cosmological and black hole spacetimes. In FRW universes with arbitrary power behavior [R(X^0) = a\;|X^0|^{\a}\, ], the asymptotic form of the solution is found for both $X^0 \to 0$ and $X^0 \to \infty$ and we plot the numerical solution for all times. Right after the big bang ($X^0 = 0$), the string energy decreasess as $R(X^0)^{-1}$ and the string size grows as $R(X^0)$ for $0 1$. Very soon [ $X^0 \sim 1$] , the ring reaches its oscillatory regime with frequency equal to the winding and constant size and energy. This picture holds for all values of \a including string vacua (for which, asymptotically, \a = 1). In addition, an exact non-oscillatory ring solution is found. For black hole spacetimes (Schwarzschild, Reissner-Nordstr\oo m and stringy), we solve for ring strings moving towards the center. Depending on their initial conditions (essentially the oscillation phase), they are are absorbed or not by Schwarzschild black holes. The phenomenon of particle transmutation is explicitly observed (for rings not swallowed by the hole). An effective horizon is noticed for the rings. Exact and explicit ring solutions inside the horizon(s) are found. They may be interpreted as strings propagating between the different universes described by the full black hole manifold.Comment: Paris preprint PAR-LPTHE-93/43. Uses phyzzx. Includes figures. Text and figures compressed using uufile

Metastable states in the Blume-Emery-Griffiths spin glass model

We study the Blume-Emery-Griffiths spin glass model in presence of an attractive coupling between real replicas, and evaluate the effective potential as a function of the density overlap. We find that there is a region, above the first order transition of the model, where metastable states with a large density overlap exist. The line where these metastable states appear should correspond to a purely dynamical transition, with a breaking of ergodicity. Differently from what happens in p-spin glasses, in this model the dynamical transition would not be the precursor of a 1-step RSB transition, but (probably) of a full RSB transition.Comment: RevTeX, 4 pages, 2 fig

Impacts of climate change on forests in different climatic zones and their implications on sustainable development

Atmospheric and meteorological data collected during the last few decades show clear evidence thatglobal climate is undergoing a long-term change. Increasing atmospheric concentrations of greenhousegases (i.e. CO" CH4, NO, and CFCs) and the consequent warming of the atmosphere are clearfeatures of' long-term climate change. Because of their long life span, these changes in climate areIikely to influence the functioning and productivity offorest ecosystems. The objective of this reviewis to predict the impacts of climate change on forests on the basis of experimental results on key plantphysiological and ecological processes.There is clear experimental evidence that increasing atmospheric CO2 (C ) increases photosynthesisand biomass production of forests. However, the magnitude of growth shmulation is likely to varywith temperature. The highest increases in productivity are expected to occur in the cooler and moistclimatic zones while the productivity increases would be lowest or absent in the warmer and drierzones. It is highly probable that the species composition offorests in all climatic zones would changebecause of the differential response of different plants species to increases in Ca and temperature.There is clear evidence that the underlying physiology of all plant species become relatively droughttolerant with increasing C . Hence, there is a possibility that in areas which are not deforested due tohuman population pressure, the existing forests would spread beyond their present boundaries withlowland evergreen forests extending to relatively drier, sub-humid climates and dryland deciduousforests extending to relatively semi-arid climates.Climate change induced changes in forests will definitely trigger changes in soil and in the complexnetwork of organisms that inhabit forests. While the inputs of carbon and nutrients to the soil throughIitter fall and root exudates are Iikely to increase with increasing Ca' soil organic matter decompositionwould also increase with increasing soil temperatures. Photosynthesis in a future high CO, environmentwill produce plant tissues with higher carbohydrates, but lower nitrogen. This will affect tlie populationsof organisms which feed on plants. Therefore, the climate change induced changes in forests couldcause wide ranging and complex secondary and tertiary effects on the whole forest ecosystem.It is well-established that management of forest resources is a vital component of sustainabledevelopment. Therefore, understanding and identifying the impacts of climate change on forestecosystems would be essential in formulating rational forest management strategies to achieve longtermsustainable development.

Mapping the CMB II: the second flight of the QMAP experiment

We report the results from the second flight of QMAP, an experiment to map the cosmic microwave background near the North Celestial Pole. We present maps of the sky at 31 and 42 GHz as well as a measurement of the angular power spectrum covering the l-range 40-200. Anisotropy is detected at about 20 sigma and is in agreement with previous results at these angular scales. We also report details of the data reduction and analysis techniques which were used for both flights of QMAP.Comment: 4 pages, with 5 figures included. Submitted to ApJL. Window functions and color figures are available at http://pupgg.princeton.edu/~cmb/welcome.htm

EVALUATION OF SLOPING AGRICUL TURAL LAND TECHNOLOGY (SALT) AS A MEANS OF ENSURING S.USU'.INABILITY OF TEA YIELDS IN THE UP-COUNTRY WET ZONE (WU2) OF SRI LANKA

Sloping Agricultural Land Technology (SACT) is a system of land management that hasbeen introduced to arrest the decline of soil fertility and sustain yields of tea plantations 0[1sloping terrain in the central highlands of Sri Lanka. SALT involves the incorporation offast-grov.ing, mostly leguminous tree species as hedgerows along contours atpre-determined distances among tea rows. The hedgerows are expected to increase soilfertility by reducing erosion and providing organic matter through frequent addition ofprunings. However, SALT hedges could compete with tea for essential growth resourcessuch as water, nutrient and light and consequently reduce tea yields. Therefore, the mainobjective of this study was to quantify the positive ana negative effects of SALT hedges andto determine their net impact on tea yields and parameters of soil fertility.Two long-term, on-farm field experiments were conducted at Helbodde Estate, Pussellawain the Up-Country Wet Zone (WU2) The effects of six tree species (Calliandracalothyrsus, Cassia spectabilis, Euphatoriun: innulifolium, Flemingia congesta, Gliricidiaseptum aid Tithonia diversifolia) growing as contour hedgerows on the long-term yields ofmature tea (ie. in the second pruning cycle) and young tea (i.e. first pruning cycle) werequantified in Experiments 1 and 2 respectively. These experiments also measured the yieldresponse to the addition of mulch material from different tree species. Continuous yieldmeasurements were done at weekly intervals since November 1998.Continuous tea yield measurements that were done at weekly intervals were compiled andanalyzed over a three-year pruning cycle from November 1998 to October, 200 1. InExperirne nt I, yield of mature tea growing with Euphatorium hedgerows was significantlygreater than the yield of tea growing without hedgerows (i.e, control plots). However,yields of .nature tea growing with all other hedgerow species were significantly lower than111 the cor.trol. Mature tea yields of all hedgerow plots increased significantly in response tothe addition of the respective hedgerow prunings as mulch. These results show thatalthough all hedgerow species contribute to the improvement of soil fertility, all hedgerowspecies except Euphatorium exert significant resource competition, whieh exceeds theirrespective positive fertility effects. In Experiment 2, yields of young tea growing with allhedgerow species, including Euphatorium showed significant reductions as compared tothe yield of sole cropped young tea. This shows that young tea is less able to withstandresource competition from hedgerows than mature tea. However, in Experiment 2, the leastyield rediction was shown in tea growing with Euphatorium. Among the differenthedgerow tree species tested, Euphatorium showed the highest yield increase due to theaddition cf prunings as mulch in both' experiments.There was significant variation in the biomass production between different hedgerow treespecies in both experiments. Calliandra and Cassia produced greater biomass than the restwhile Glir'cidia and Euphatorium produced lower biomass levels. In both experiments,there were moderately strong negative relationships between tea yield and hedgerowbiomass. This is a confirmation that higher biomass production by the hedgerows increasestheir resource u~e and decreases tea yields.Detailed analysis of soil chemical and physical properties showed significant variationbetween S/,L T systems with different hedgerow species and between mulching treatments.In mature lea, the soil N, P and K contents were lower in SALT plots than in sole leacrops. In young tea, while most of the SALT plots had higher soil N than the control, bothP and K in SALT plots were lower than in the control. In both mature and young tea, soilCa was lower in SALT systems than in the control- In contrast, soil Mg in the majority ofSALT plots was lower than the control in mature tea while the opposite was observed inyoung tea. !n both mature and young tea, the majority of SALT systems had a lower soilpH than the control plots. However, the SALT systems of both mature and young tea had ahigher soil cation exchange capacity (C~C) and organic matter (OM) content than therespective sole tea crops. In SALT plots with both mature and young tea, mulchingsignificantly increased soil N, P, K, Ca, Mg, CEC and OM. However, soil pH did notchange sigr ificantIy due to mulching. Multiple regression' analysis showed that 87% of theobserved yield variation of mature tea in SALT systems could be explained by the variationof the above soil properties. In SALT systems with young tea, 98% of the yield variationcould be explained by the variation of soil properties.Based on the above results of these two long-term experiments, it is concluded thatincorporatic n of tree hedges in existing tea fields have to be done with caution as it coulddecrease tea yields due to excessive resource competition. However, SALT systems showedsome positive indicators such as greater soil organic matter and cation exchange capacity,which may contribute to long-term increase of soil fertility and sustainability of tea yieldson sloping terrain in the central highlands of Sri Lanka. 

Avaliação de cultivares de milho precoce em alguns estados do Nordeste brasileiro.

bitstream/item/88596/1/CPATC-PESQ.-AND.-27-84.pd

Bicudo e lagarta-rosada em algodoeiros no sertão sergipano.

bitstream/CPATC/19936/1/ct-52.pd

VARIATION OF STOMATAL CONDUCTANCE AND ITS CONTROLLING FACTORS OF DIFFERENT SPECIES IN A WET EVERGREEN FOREST IN THE MID·COUNTRY WET ZONE OF SRI LANKA

Stomatal conductance is a primary determinant of the net carbon balance and growth of differentplant species in a forest community. Because of its influence on transpirational water loss, stomatalconductance determines the water balance of a plant. As both carbon and water balances playimportant roles in survival and establishment of seedlings of different plant species in a forestcommunity, stomatal conductance has a direct influence on species composition and succession of aforest. Therefore, the main objective of the present study was to describe the inter-species variationof stomatal conductance in a wet, evergreen forest in the mid-country wet zone of Sri Lanka. Asecondary objective was to examine the variation of two parameters which could influence stomatalopening, namely incident light intensity and leaf temperature, and to see whether any directcorrelations can be established between stomatal conductance and the above parameters.This study was conducted in the Gannoruwa forest reserve in Kandy in September, 1997. 108 plantspecies which included all growth forms (i.e. trees, shrubs, herbaceous plants, vines and grasses)were found. Stomatal conductance was measured using a portable diffusion porometer which alsorecorded the incident light intensity ( in terms of photosynthetically-active radiation) and leaftemperature. Conductances of both upper and lower leaf surfaces were measured and total leafconductance was obtained by summing the two above measurements. In a given species, at leastthree plants were sampled.There were significant differences between species in lower surface conductance (gi), upper surfaceconductance (gu) and total leaf conductance (g). Except in one species, gl was greater than gu in allother species examined. Lower Surface Conductance/g, ) ranged from 17 to 1280 mmol m,2 S'I with amean of 175.8 += 8.9 mmol m ,2S'I whereas gu ranged from 2.36 to 252 mmol m,2 S'I with a mean of25.15 += 1.58 mmol m,2 S'I. The range of total conductance (g) was 20.45 - 1309.8 mmol m,2 S'Iwith a mean of 20 1.41 += 9.44 nunol m,2 S'I. The frequency distributions of aH three conductanceparameters (i.e. lower, upper and total) were skewed to the left with the respective median valuesbeing 132.5 (for gr ), 18.25 (gu) and 149.9 (g) mmol rn" S'I . Normality of the distributions whentested using the box plot technique, showed significant skewness to the left, Deletion of extremevalues did not improve normality significantly.The light intensities experienced by the leaves ranged from 2.5 to 1830 umol (PAR) m ,2S'I and theleaf temperatures ranged from 24.55 to 34.40 C. When all species were considered together, totalleaf stomatal conductance (g) had a significant positive correlation with light intensity. But, therewas no significant correlation between g and leaf temperature. Similar results were obtained whenlower and upper surface conductances were considered separately as well. There was a highlysignificant positive correlation between light intensity and leaf temperature. A multiple regressionanalysis showed that these two variables explained only 8% of the overall variation of leaf stomatalconductance. This infers species differences, interactions between species, and their response tovariations in light intensity and leaf temperature are more significant. Stomatal conductance ofditTerent species respond in ditTerent degrees to light and temperature variations.1\ cluster analysis allowed the 108 plant species examined to be grouped in to different categorieson the basis of their total leaf stomatal conductance (g). The different species groups could bebroadly related to their position in the successional sequence. It was found that the speciesestablished under the canopy on the forest floor generally had lower levels of g than thoseestablishing in canopy gaps. While many species of the latter group (growing in gaps) had the abilityto raise their stomatal conductance in response to increasing light intensity, most species of theformer group (growing under the canopy shade) could not respond to the occasional sunflecks thatare incident on them at different times of the day.