A geometrical derivation of the Dirac equation

We give a geometrical derivation of the Dirac equation by considering a spin-1/2 particle travelling with the speed of light in a cubic spacetime lattice. The mass of the particle acts to flip the multi-component wavefunction at the lattice sites. Starting with a difference equation for the case of one spatial and one time dimensions, we generalize the approach to higher dimensions. Interactions with external electromagnetic and gravitational fields are also considered. One logical interpretation is that only at the lattice sites is the spin-1/2 particle aware of its mass and the presence of external fields.Comment: 9 pages, LaTeX, version accepted for publication in Phys. Lett.

Geography of Production Linkages in the Irish and Scottish Microcomputer Industry: The Role of Logistics

The economic crisis of the mid-1970s marked the transition from the traditional Fordist mode of industrial organization to one of time-based competition (TBC). It has been postulated that the rise of TBC will lead to an increase in local and regional production linkages. Part of the argument is that the associated search for logistical efficiency and the adoption of the just-in-time (JIT) principles will lead to closer buyer-supplier proximity. In this article, we test the relevance of this idea in a case study of the microcomputer hardware industry in Ireland and Scotland. Most of the data were collected during multiple interviews with subsidiaries of all global microcomputer assemblers with operations in one of the two countries. The study shows that rather than sourcing locally or regionally, the assemblers import the vast majority of their material inputs from regions outside Ireland and Britain, notably from the Far East, and that the inbound logistics pipelines of most components involve inventories, often hubbed in local warehouses. Such supply systems have been interpreted as pseudo-JIT, suboptimal inbound logistics systems that are organized on traditional Fordist principles. We argue that the logistics systems and the geography of the supply linkages should not be interpreted this way. Inbound inventories were tightly managed, leading to modest target buffer levels and high shipment frequencies. Even under JIT supply, the geographic configuration of production linkages and the details of logistics systems remain highly dependent on a range of contextual conditions and component characteristics. The findings of this study suggest that a strategy of building integrated vertical production clusters around subsidiaries of multinational enterprises is no longer suitable for Ireland and Scotland, at least not in the context of the microcomputer industry

Synthesis and evaluation of N⁶-substituted apioadenosines as potential adenosine A₃ receptor modulators

Adenosine receptors (ARs) trigger signal transduction pathways inside the cell when activated by extracellular adenosine. Selective modulation of the A(3)AR subtype may be beneficial in controlling diseases such as colorectal cancer and rheumatoid arthritis. Here, we report the synthesis and evaluation of beta-D-apio-D-furano- and alpha-D-apio-L-furanoadenosines and derivatives thereof. Introduction of a 2-methoxy-5-chlorobenzyl group at N-6 of beta-D-apio-D-furanoadenosine afforded an A(3)AR antagonist (10c, K = 0.98 mu M), while a similar modification of an alpha-D-apio-L-furanoadenosine gave rise to a partial agonist (11c, K-i = 3.07 mu M). The structural basis for this difference was examined by docking to an A(3)AR model; the antagonist lacked a crucial interaction with Thr94

Supersymmetry algebra in N = 1 chiral supergravity

We consider the supersymmetry (SUSY) transformations in the chiral Lagrangian for $N = 1$ supergravity (SUGRA) with the complex tetrad following the method used in the usual $N = 1$ SUGRA, and present the explicit form of the SUSY trasformations in the first-order form. The SUSY transformations are generated by two independent Majorana spinor parameters, which are apparently different from the constrained parameters employed in the method of the 2-form gravity. We also calculate the commutator algebra of the SUSY transformations on-shell.Comment: 10 pages, late

Aspen Soils Retain More Dissolved Organic Carbon Than Conifer Soils in a Sorption Experiment

The effect tree species have on soil organic carbon (SOC) has been hotly debated but, so far, few clear patterns have emerged. One example of a differing tree species effect on SOC is aspen forests in North America, which have been found to have more stable SOC than adjacent conifer forest stands. An important source for the formation of stable organo-mineral complexes in the soil is dissolved organic carbon (DOC). DOC concentrations in mineral soil are often higher under the thick O-horizons of conifer forests than under aspen forests, but this does not correspond to more stable mineral SOC. This suggests that, instead of DOC concentration, DOC quality could be driving the observed differences in SOC. Therefore, we quantified the retention of contrasting forest detritus DOC in soils. Using a batch sorption experiment approach, we compared the retention of detritus leachates from four sources – aspen leaves (AL), aspen roots (AR), conifer (subalpine fir) needles (CN), and conifer (subalpine fir) roots (CR) – on soils sampled under aspen and conifer (subalpine fir and Douglas fir) overstories. The calculated sorption isotherms showed higher retention of AL DOC than AR DOC, as indicated by all four sorption parameters – k and n (curve-fitting parameters), null point concentration (NPC; net sorption = net desorption), and endpoint (EP, retention at the highest initial DOC concentration). Leachates from CN and CR showed very similar retention behavior, and between the two species, the retention of root leachates was more similar than the retention of foliage leachates. Soils sampled from aspen forests showed a higher affinity for new DOC than conifer soils [higher sorption rate (n), lower NPC, and higher EP] regardless of the DOC source. The findings suggest that the higher DOC sorption on aspen soils might be a major driver for more stable SOC under aspen stands in North America

Probabilistic Clustering of Sequences: Inferring new bacterial regulons by comparative genomics

Genome wide comparisons between enteric bacteria yield large sets of conserved putative regulatory sites on a gene by gene basis that need to be clustered into regulons. Using the assumption that regulatory sites can be represented as samples from weight matrices we derive a unique probability distribution for assignments of sites into clusters. Our algorithm, 'PROCSE' (probabilistic clustering of sequences), uses Monte-Carlo sampling of this distribution to partition and align thousands of short DNA sequences into clusters. The algorithm internally determines the number of clusters from the data, and assigns significance to the resulting clusters. We place theoretical limits on the ability of any algorithm to correctly cluster sequences drawn from weight matrices (WMs) when these WMs are unknown. Our analysis suggests that the set of all putative sites for a single genome (e.g. E. coli) is largely inadequate for clustering. When sites from different genomes are combined and all the homologous sites from the various species are used as a block, clustering becomes feasible. We predict 50-100 new regulons as well as many new members of existing regulons, potentially doubling the number of known regulatory sites in E. coli.Comment: 27 pages including 9 figures and 3 table

Where Have All the Students Gone? Strategies for Tackling Falling Enrollments

As most of us are well aware, enrollments in information technology-related academic programs have declined sharply since the late 1990\u27s. This paper addresses possible causes of the enrollment decline, and dispels myths regarding IT-related careers. The authors report on a number of efforts underway at various universities to redesign core curriculum and develop secondary programs. They also describe marketing and promotion approaches undertaken by universities and professional organizations in the field. Finally, the authors call for more cooperative and coordinated efforts to address the underlying problems that have led to the current enrollment declines

Note on Possible Emergence Time of Newtonian Gravity

If gravity were an emergent phenomenon, some relativistic as well as non-relativistic speculations claim it is, then a certain emergence time scale tau_? would characterize it. We argue that the available experimental evidences have poor time resolution regarding how immediate the creation of Newton field of accelerated mass sources is. Although the concrete theoretical model of gravity's `laziness' is missing, the concept and the scale tau_? ~ 1ms, rooted in an extrapolation of spontaneous wave function collapse theory, might be tested directly in reachable experiments.Comment: 2pp, essentially revised, clarified, concretized version accepted in PL