Stripe orientation in an anisotropic t-J model

The tilt pattern of the CuO_6 octahedra in the LTT phase of the cuprate superconductors leads to planar anisotropies for the exchange coupling and hopping integrals. Here, we show that these anisotropies provide a possible structural mechanism for the orientation of stripes. A t_x-t_y-J_x-J_y model thus serves as an effective Hamiltonian to describe stripe formation and orientation in LTT-phase cuprates.Comment: 3 pages, 3 figure

CQESTR Simulation of Management Practice Effects on Long-Term Soil Organic Carbon

Management of soil organic matter (SOM) is important for soil productivity and responsible utilization of crop residues for additional uses. CQESTR, pronounced “sequester,” a contraction of “C sequestration” (meaning C storage), is a C balance model that relates organic residue additions, crop management, and soil tillage to SOM accretion or loss. Our objective was to simulate SOM changes in agricultural soils under a range of climate and management systems using the CQESTR model. Four long-term experiments (Champaign, IL, \u3e100 yr; Columbia, MO, \u3e100 yr; Lincoln, NE, 20 yr; Sidney, NE, 20 yr) in the United States under various crop rotations, tillage practices, organic amendments, and crop residue removal treatments were selected for their documented history of the long-term effects of management practice on SOM dynamics. CQESTR successfully simulated a substantial decline in SOM with 50 yr of crop residue removal under various rotations at Columbia and Champaign. The increase in SOM following addition of manure was simulated well; however, the model underestimated SOM for a fertilized treatment at Columbia. Predicted and observed values from the four sites were signifi cantly related (r2 = 0.94, n = 113, P \u3c 0.001), with slope not signifi cantly different from 1. Given the high correlation of simulated and observed SOM changes, CQESTR can be used as a reliable tool to predict SOM changes from management practices and offers the potential for estimating soil C storage required for C credits. It can also be an important tool to estimate the impacts of crop residue removal for bioenergy production on SOM level and soil production capacity

D-instantons probing D3-branes and the AdS/CFT correspondence

D-instantons are considered as a probe of coinciding $N$ D3-branes. They can feel an external metric via the commutator terms in their effective action. We show that when the D-instantons are separated from the D3-branes, the metric which is probed at the one loop level, {\it exactly} coincides with that of the BPS R-R 3-brane. Interesting connection of this result to the possible explanation of the AdS/CFT correspondence within IKKT M-atrix theory is discussed.Comment: 8pp., Latex. Minor changes, misprints are correcte

Incorporating Distributed Debris Thickness in a Glacio-Hydrological Model: Khumbu Himalaya, Nepal

Understanding the future evolution of Himalayan glaciers is important in terms of runoff that provides an essential water source to local populations and has far-reaching downstream impacts. However, the climatic response of glaciers in High-Mountain Asia is complicated by ice stagnation and considerable supraglacial debris coverage, which insulates the ice from warming. Typical runoff modelling only crudely incorporates debris cover and there is currently no consensus on how significantly this may impact future glacier and runoff evolution. Here, a glacio-hydrological model is modified to incorporate fully distributed debris cover, using melt reduction factors that vary depending on debris thickness, and to redistribute mass losses according to observed surface elevation changes. A range of debris thickness data are implemented, including a remote-sensing survey and a modelled debris surface, to analyse the sensitivity of glacier evolution and runoff to possible future debris-cover changes in a series of experiments in the upper Khumbu catchment, Nepal. Simulations are undertaken using climate input data from Regional Climate Model simulations from CORDEX (Coordinated Regional Downscaling Experiment) which are further statistically downscaled using data from the Pyramid meteorological station. Results suggest that the accurate calibration of the model to volume change compensates for the inclusion of distributed debris cover but only if the climatic sensitivity of the calibration period (1999–2010) and the nature of the debris-covered surface remain constant during future simulations. Altering the nature of the debris surface has a significant impact on simulated ice volume, with melt rates under debris suppressed by up to 85 %. The sensitivity of runoff ranges from 60 to 140 million m3 yr-1, although there are considerable uncertainties relating to non-glacial snow melt. Moreover, incorporating locally enhanced melt at ice cliffs into the model also impacts upon volume loss and discharge, with a greater proportion of ice cliffs leading to enhanced volume losses compared to a homogeneous debris surface. Finally, using the most representative model configuration, the future evolution of Khumbu Glacier under various climate scenarios shows continued mass losses with a reduction in volume ranging from 60 % to 97 % by 2100. Runoff trends show an initial increase followed by an eventual decrease, with runoff in 2100 predicted to be 8 % lower than current levels

Exactly Marginal Deformations of N=4 SYM and of its Supersymmetric Orbifold Descendants

In this paper we study exactly marginal deformations of field theories living on D3-branes at low energies. These theories include N=4 supersymmetric Yang-Mills theory and theories obtained from it via the orbifolding procedure. We restrict ourselves only to orbifolds and deformations which leave some supersymmetry unbroken. A number of new families of N=1 superconformal field theories are found. We analyze the deformations perturbatively, and also by using general arguments for the dimension of the space of exactly marginal deformations. We find some cases where the space of perturbative exactly marginal deformations is smaller than the prediction of the general analysis at least up to three-loop order), and other cases where the perturbative result (at low orders) has a non-generic form.Comment: 25 pages, 1 figure. v2: added preprint number, references adde

Monopyrroles in porphyria and related disorders

The hereditary porphyrias are a group of disorders in which the genetic defect results in an abnormality in the biosynthetic pathway leading to the respiratory pigment haem. The characteristic result of this is excessive synthesis and excretion of the tetrapyrrolic porphyrins sind, in the acute porphyrias, their precursors 6-aminolaevulinic acid (ALA.) and porphobilinogen. The acute attacks of acute porphyria show certain similarities to psychiatric disorders and the finding of a pyrrolic metabolite in the urine of patients with acute intermittent porphyria (AIP) and certain psychiatric disorders was the common factor that implicated this metabolite in the aetiology of certain manifestations of these disorders. Identification of the metabolite proved difficult but it was eventually unambiguously identified as 3-ethyl-5-hydroxy-4,5-dimethyl-Δ3-pyrrolin-2-one (OHHPL). The work contained in this thesis describes clinical and biochemical investigations into the occurrence and properties of this compound. Initially a qualitative method was used to detect OEHPL and it was shown to be present in the urine of patients with acute porphyria in attack and remission but to be undetectable in patients who were latent for the disease. Using a gas-liquid chromatography method developed for the quantitative assay of OHHPL, it was shown that in carriers of the AIP gene defect there was no significant difference in OHHPL excretion in latency, attack and remission, but that levels in these patients were significantly greater than in control subjects. No correlation could be shown between OHHPL excretion and clinical condition either in the group of patients or in multiple estimations in single patients. However, a significant association was found between the excretion of OHHPL and that of ALA. and PBG and it was also shown that in the porphyric patients ALA and PBG excretion were related in a linear fashion. Quantitation of OHHPL in groups of psychiatric patients showed that there was a significant elevation of OHHPL excretion in psychotic patients who were undergoing drug therapy and also in groups of patients with schizophrenia and organic brain disease. In the patients with schizophrenia there was a negative correlation between the clinical condition of the patients as assessed on the Hamilton-Lorr rating scale and urinary OHHPL. In an attempt to exatmine further the relationship between OHHPL and PBG and ALA in the patients with porphyria a group of patients, industrial lead workers, with sub-clinical lead poisoning were studied. These patients had raised blood lead and increased urinary excretion of ALA resulting from an inhibition by lead of the enzyme 6-aminolaevulinic acid dehydratase (ALA.D). OKHPL and PBG concentrations in the urine of these workers were within the normal range. It was found that there was a negative association between OHHPL and ALA levels which suggested that the ALA-OHHPL association in the porphyric patients was purely a result of the ALA-PBG relationship

Aspects of Open-Closed Duality in a Background B-Field

We study closed string exchanges in background $B$-field. By analysing the two point one loop amplitude in bosonic string theory, we show that tree-level exchange of lowest lying, tachyonic and massless closed string modes, have IR singularities similar to those of the nonplanar sector in noncommutative gauge theories. We further isolate the contributions from each of the massless modes. We interpret these results as the manifestation of open/closed string duality, where the IR behaviour of the boundary noncommutative gauge theory is reconstructed from the bulk theory of closed strings.Comment: 33 pages, 4 figures, v2:references added, v3: minor changes, typos corrected, references adde

Noncritical String Correlators, Finite-N Matrix Models and the Vortex Condensate

We carry out a systematic study of correlation functions of momentum modes in the Euclidean c=1 string, as a function of the radius and to all orders in perturbation theory. We obtain simple explicit expressions for several classes of correlators in terms of special functions. The Normal Matrix Model is found to be a powerful calculational tool that computes c=1 string correlators even at finite N. This enables us to obtain a simple combinatoric formula for the 2n-point function of unit momentum modes, which after T-duality determines the vortex condensate. We comment on possible applications of our results to T-duality at c=1 and to the 2d black hole/vortex condensate problem.Comment: 38 pages, LaTe