Responses of soybean ancestral lines and cultivars to simulated acid rain

During 1985, 1986, and 1987, field and greenhouse experiments were conducted on four ancestral lines and two cultivars from each of the northern and southern gene pools. The ancestral lines have contributed approximately 80% of the genes to their respective gene pools. Representatives from the northern germplasm collection included Mandarin, Manchu, AK Harrow, Richland, \u27Amsoy 71\u27, and \u27Williams 82\u27. The southern germplasm collection was represented by CNS, S 100, PI 54610, Tokyo, \u27Lee 74\u27, and \u27Essex\u27. Spray-to-wet applications of simulated acid rain (SAR) were applied at three acidity levels (pH 2.8, 3.2, and 4.3). Field experiments were grown under optimum and sub-optimum soil conditions (pH and fertility) at two diverse locations to determine if soybean response to SAR was affected by edaphic factors. In general, SAR had no effect on seed yield. In cases where yield was affected, there were more positive than negative effects. There was no consistent trend with respect to optimum vs sub-optimum soil conditions. Seed weight was affected by SAR for some lines but was not necessarily related to yield. In general, photosynthesis, transpiration, and stomatal frequency were not affected by SAR. Early stages of plant growth (leaf and stem weight) in the greenhouse was affected by SAR, but measurements taken on the same characteristics during later growth stages were not significant. These results indicate that soybean cultivars in general will not be detrimentally affected by acid rain based on the response of their ancestral lines and evaluations of selected cultivars derived from them

Multiple parton interactions in high-density QCD matter

Multiple interactions of quarks and gluons in high-energy heavy-ion collisions may give rise to interesting phemomena of color charges propagating in high-density QCD matter. We study the dynamics of multi-parton systems produced in nucleus-nucleus collisions at energies corresponding the the CERN SPS and the future BNL RHIC experiments. Due to the complexity of the multi-particle dynamics we choose to employ the parton cascade model in order to simulate the development of multiple parton scatterings and associated stimulated emision processes. Our results indicate a non-linear increase with nuclear mass A of, e.g., parton multiplicity, energy density, strangeness, and contrast a linear A-scaling as in Glauber-type approaches. If multiple interactions are suppressed and only single parton scatterings (no re-interactions) are considered, we recover such a linear behavior. It remains to be studied whether these results on the parton level can be experimentally seen in final-state observables, such as the charged particle multiplicity, the magnitude of produced transverse energy, or the number of produced strange hadrons.Comment: 15 pages including 9 postscript figure

Thermodynamic versus statistical nonequivalence of ensembles for the mean-field Blume-Emery-Griffiths model

We illustrate a novel characterization of nonequivalent statistical mechanical ensembles using the mean-field Blume-Emery-Griffiths (BEG) model as a test model. The novel characterization takes effect at the level of the microcanonical and canonical equilibrium distributions of states. For this reason it may be viewed as a statistical characterization of nonequivalent ensembles which extends and complements the common thermodynamic characterization of nonequivalent ensembles based on nonconcave anomalies of the microcanonical entropy. By computing numerically both the microcanonical and canonical sets of equilibrium distributions of states of the BEG model, we show that for values of the mean energy where the microcanonical entropy is nonconcave, the microcanonical distributions of states are nowhere realized in the canonical ensemble. Moreover, we show that for values of the mean energy where the microcanonical entropy is strictly concave, the equilibrium microcanonical distributions of states can be put in one-to-one correspondence with equivalent canonical equilibrium distributions of states. Our numerical computations illustrate general results relating thermodynamic and statistical equivalence and nonequivalence of ensembles proved by Ellis, Haven, and Turkington [J. Stat. Phys. 101, 999 (2000)].Comment: 13 pages, 4 figures, minor typos corrected and one reference adde

Kinematics of deformable media

We investigate the kinematics of deformations in two and three dimensional media by explicitly solving (analytically) the evolution equations (Raychaudhuri equations) for the expansion, shear and rotation associated with the deformations. The analytical solutions allow us to study the dependence of the kinematical quantities on initial conditions. In particular, we are able to identify regions of the space of initial conditions that lead to a singularity in finite time. Some generic features of the deformations are also discussed in detail. We conclude by indicating the feasibility and utility of a similar exercise for fluid and geodesic flows in flat and curved spacetimes.Comment: 28 pages, 12 figure

Vacuum-Induced Quantum Decoherence and the Entropy Puzzle

Or: ``How to generate an ensemble in a single event?'' Following recent work on entropy in strong interactions, I explain the concept of environment-induced quantum decoherence in elementary quantum mechanics. The classically chaotic inverted oscillator becomes partially decoherent already in the environment of a single other oscillator performing only vacuum fluctuations. One finds exponential entropy growth in the subsystem with a Lyapunov exponent, which approaches the classical one for weak coupling. Presented at the Workshops on ``Quantum Infrared Physics'', Paris, 6 - 10.6.94, and ``QCD 94'', Montpellier, 7 - 13.7.94. Invited talk at the NATO Adv. Res. Workshop on ``Hot Hadronic Matter'', Divonne, 27.6. - 1.7.94. To appear in the Proceedings.Comment: 12 pages, CERN-TH.7372/9

Can Cosmic Ray Catalysed Vacuum Decay Dominate Over Tunnelling?

We consider the question of whether cosmic ray catalysed false vacuum decay can be phenomenologically more important than spontaneous decay via quantum tunnelling. We extend the zero bubble wall width Landau-WKB analysis of catalysed false vacuum decay to include the leading order effects of finite wall width and derive an expression for the thin-wall bubble action. Using this we calculate the exponential suppression factor for the catalysed decay rate at the critical bubble energy, corresponding to the largest probability of catalysed decay. We show that, in general, cosmic ray catalysed decay is likely to be more important than spontaneous decay for sufficiently thin-walled bubbles (wall thickness less than about 30 % of the initial bubble radius), but that spontaneous decay will dominate for the case of thick-walled bubbles. Since any perturbative model with a cosmologically significant false vacuum decay rate will almost certainly produce thick-walled bubbles, we can conclude that cosmic ray catalysed false vacuum decay will never dominate over tunnelling in imposing phenomenological constraints on perturbative particle physics models.Comment: 22 pages Latex, 3 figures include

Reality and causality in quantum gravity modified electrodynamics

We present a general description of the propagation properties of quantum gravity modified electrodynamics characterized by constitutive relations up to second order in the correction parameter. The effective description corresponds to an electrodynamics in a dispersive and absorptive non-local medium, where the Green functions and the refraction indices can be explicitly calculated. The reality of the electromagnetic field together with the requirement of causal propagation in a given referrence frame leads to restrictions in the form of such refraction indices. In particular, absorption must be present in all cases and, contrary to the usual assumption, it is the dominant aspect in those effective models which exhibit linear effects in the correction parameter not related to birefringence. In such a situation absorption is linear while propagation is quadratical in the correction parameter.Comment: 15 pages, LaTex, minor changes to clarify some points, version accepted for publicatio

Role of longitudinal fluctuations in L10 FePt

L10 FePt is a technologically important material for a range of novel data storage applications. In the ordered FePt structure the normally nonmagnetic Pt ion acquires a magnetic moment, which depends on the local field originating from the neighboring Fe atoms. In this work a model of FePt is constructed in which the induced Pt moment is simulated by using combined longitudinal and rotational spin dynamics. The model is parameterized to include a linear variation of the moment with the exchange field, so that at the Pt site the magnetic moment depends on the Fe ordering. The Curie temperature of FePt is calculated and agrees well with similar models that incorporate the Pt dynamics through an effective Fe-only Hamiltonian. By computing the dynamic correlation function the anisotropy field and the Gilbert damping are extracted over a range of temperatures. The anisotropy exhibits a power-law dependence on the magnetization with exponent n≈2.1. This agrees well with what was observed experimentally, and it is obtained without including a two-ion anisotropy term as in other approaches. Our work shows that incorporating longitudinal fluctuations into spin dynamics calculations is crucial for understanding the properties of materials with induced moments

Scattering and Resonances in QCD_2

Extending previous works on the spectrum of QCD_2, we now investigate the 2D analogue of meson-baryon scattering. We use semi-classical methods, perturbing around classical soliton solutions. We start with the abelian case, corresponding to one flavor,and find that in this case the effective potential is reflectionless. We obtain an explicit expression for the forward phase shift. In the non-abelian case of several flavors, the method yields a potential which depends on the momentum of the incoming particle. In this case there is both transmission and reflection. In both cases no resonances appear. As a byproduct, we derive the general conditions for a 2D quantum field theoretical action to yield a reflectionless effective potential when one expands in small fluctuations about the classical solution.Comment: Figs. 2 and 3 and the accompanying text amended, following sign correction in the first term in the potential V in eq. (58). Qualitative conclusions unchange

Perfect magnetohydrodynamics as a field theory

We propose the generally covariant action for the theory of a self-coupled complex scalar field and electromagnetism which by virtue of constraints is equivalent, in the regime of long wavelengths, to perfect magnetohydrodynamics (MHD). We recover from it the Euler equation with Lorentz force, and the thermodynamic relations for a prefect fluid. The equation of state of the latter is related to the scalar field's self potential. We introduce 1+3 notation to elucidate the relation between MHD and field variables. In our approach the requirement that the scalar field be single valued leads to the quantization of a certain circulation in steps of $\hbar$; this feature leads, in the classical limit, to the conservation of that circulation. The circulation is identical to that in Oron's generalization of Kelvin's circulation theorem to perfect MHD; we here characterize the new conserved helicity associated with it. We also demonstrate the existence for MHD of two Bernoulli-like theorems for each spacetime symmetry of the flow and geometry; one of these is pertinent to suitably defined potential flow. We exhibit the conserved quantities explicitly in the case that two symmetries are simultaneously present, and give examples. Also in this case we exhibit a new conserved MHD circulation distinct from Oron's, and provide an example.Comment: RevTeX, 16 pages, no figures; clarifications added and typos corrected; version to be published in Phys. Rev.