Real time correlations at finite Temperature for the Ising model

After having developed a method that measures real time evolution of quantum systems at a finite temperature, we present here the simplest field theory where this scheme can be applied to, namely the 1+1 Ising model. We will compute the probability that if a given spin is up, some other spin will be up after a time $t$, the whole system being at temperature $T$. We can thus study spatial correlations and relaxation times at finite $T$. The fixed points that enable the continuum real time limit can be easily found for this model. The ultimate aim is to get to understand real time evolution in more complicated field theories, with quantum effects such as tunneling at finite temperature.Comment: 3 pp in Latex, 2 ps Figs., presented at the Latt98 Conf. in Boulder C

Energy-Efficient NoC for Best-Effort Communication

A Network-on-Chip (NoC) is an energy-efficient on-chip communication architecture forMulti-Processor System-on-Chip (MPSoC) architectures. In an earlier paper we proposed a energy-efficient reconfigurable circuit-switched NoC to reduce the energy consumption compared to a packetswitched NoC. In this paper we investigate a chordal slotted ring and a bus architecture that can be used to handle the best-effort traffic in the system and configure the circuitswitched network. Both architectures are compared on their latency behavior and power consumption. At the same clock frequency, the chordal ring has the major benefit of a lower latency and higher throughput. But the bus has a lower overall power consumption at the same frequency. However, if we tune the frequency of the network to meet the throughput requirements of control network, we see that the ring consumes less energy per transported bit

Modelling of the diffusion of carbon dioxide in polyimide matrices by computer simulation

Computer aided molecular modelling is used to visualize the motion of CO2 gas molecules inside a polyimide polymer matrix. The polymers simulated are two 6FDA-bases polyimides, 6FDA-4PDA and 6FDA-44ODA. These polymers have also been synthesized in our laboratory, and thus the simulated properties could directly be compared with “real-world” data. The simulation experiments have been performed using the GROMOS1 package. The polymer boxes were created using the soft-core method, with short (11 segments) chains. This results in highly relaxed and totally amorphous polyimide matrices. The motion of randomly placed CO2 molecules in the boxes during molecular dynamics runs was followed, revealing three types of motion: jumping, continuous- and trapped motion. The calculated diffusivities are unrealistic, but possible shortcomings in our model are given

Fermion Number Conservation Isn't Fermion Conservation

A nonperturbative regularization of the Standard Model may have a superficially undesirable exact global U(1) symmetry corresponding to exact fermion number conservation. We argue that such a formulation can still have the desired physics of fermion nonconservation, i.e. fermion particle creation and annihilation by sphaleron transitions. We illustrate our reasoning in massless axial QED in 1+1 dimensions.Comment: 3 pages to appear in the proceedings of Lattice '93, Dallas, Texas, 12-16 October 1993, comes as a single uuencoded postscript file (LaTeX source available from the authors), ITFA 93-3

Psalm 151 — uit Septuaginta en Qumran*

Psalm 151? Nog nooit van gehoor nie? Daar is mos maar net presies 150 Psalms. So is ons dit al die jare al gewoond. Dit is natuurlik waar ook. Die Bybel bevat presies 150 kanonieke Psalms. Om dit anders te stel: in die kanon van die O.T. is daar 150 psalms in die boek Psalms opgeneem. Hierdie psalms kom ook in beryming voor soos ons dit tans in die kerk sing. Naas die psalms sing die Afrikaanse kerke ook „gesange” en „Skrifberymings”, maar ons sal dit nooit waag om een hiervan ook „psalm” te noem nie

Fermion production despite fermion number conservation

Lattice proposals for a nonperturbative formulation of the Standard Model easily lead to a global U(1) symmetry corresponding to exactly conserved fermion number. The absence of an anomaly in the fermion current would then appear to inhibit anomalous processes, such as electroweak baryogenesis in the early universe. One way to circumvent this problem is to formulate the theory such that this U(1) symmetry is explicitly broken. However we argue that in the framework of spectral flow, fermion creation and annihilation still in fact occurs, despite the exact fermion number conservation. The crucial observation is that fermions are excitations relative to the vacuum, at the surface of the Dirac sea. The exact global U(1) symmetry prohibits a state from changing its fermion number during time evolution, however nothing prevents the fermionic ground state from doing so. We illustrate our reasoning with a model in two dimensions which has axial-vector couplings, first using a sharp momentum cutoff, then using the lattice regulator with staggered fermions. The difference in fermion number between the time evolved state and the ground state is indeed in agreement with the anomaly. A study of the vacuum energy shows that the perturbative counterterm needed for restoration of gauge invariance is insufficient in a nonperturbative setting. For reference we also study a closely related model with vector couplings, the Schwinger model, and we examine the emergence of the $\theta$-vacuum structure of both theories.Comment: 31 pages, LaTeX + uuencoded figs file (=5 PS figs). UvA-ITFA 94-17, UCSD/PTH 94-0

KOERS op pad

Dit is 'n gevestigde tradisie van KOERS dat daar geen redaksionele skrywes aan die lesers gerig word nie, behalwe met die verskyning van dié nommers wat 'n besondere mylpaal aandui. Hierdie keer is die mylpaal die betrekking van 'n besondere vennoot. Die lesers mag dit van meet af aan gerus weet dat die pad nog dieselfde is as dié van 1933 met die verskyning van die eerste uitgawe, en soos telkens later herbevestig: die grondslag is die Heilige Skrif, en die doel is om die beginsels van God se Woord volgens die interpretasie van die Calvinisme te propageer op die verskillende lewensterreine

Hearts in sight – A pretty picture of collapse and excellence

A surprising number of serious decisions in the history of nations and populations have been firmly based upon generalisations, speculation, popular opinion and unproven theories. It is very much like guessing the weight and height of a patient and then calculating his body surface area to the second decimal, like old perfusionists did, and then basing the required pump flow rates on this calculation. The funny thing is that the patients were mostly fine. So, I trust that most of you will survive the generalisations and opinions expressed in this editorial