145 research outputs found
Two-Dimensional Cutting Problem
This paper deals with two-dimensional cutting problems. Firstly the complexity of the problem in question is estimated. Then, several known approaches for the regular (rectangular) and irregular (not necessarily rectangular) cutting problems are described. In the second part, a decision support system for cutting a rectangular sheet of material into pieces of arbitrary shapes, is presented. The system uses two earlier described methods which prefer different types of data and the user may decide which one is more suitable for the problem in question. After brief description of system data files and its manual, some experimental results are presented
Precision mass measurements of magnesium isotopes and implications on the validity of the Isobaric Mass Multiplet Equation
If the mass excess of neutron-deficient nuclei and their neutron-rich mirror
partners are both known, it can be shown that deviations of the Isobaric Mass
Multiplet Equation (IMME) in the form of a cubic term can be probed. Such a
cubic term was probed by using the atomic mass of neutron-rich magnesium
isotopes measured using the TITAN Penning trap and the recently measured
proton-separation energies of Cl and Ar. The atomic mass of
Mg was found to be within 1.6 of the value stated in the Atomic
Mass Evaluation. The atomic masses of Mg were measured to be both
within 1, while being 8 and 34 times more precise, respectively. Using
the Mg mass excess and previous measurements of Cl we uncovered a
cubic coefficient of = 28(7) keV, which is the largest known cubic
coefficient of the IMME. This departure, however, could also be caused by
experimental data with unknown systematic errors. Hence there is a need to
confirm the mass excess of S and the one-neutron separation energy of
Cl, which have both come from a single measurement. Finally, our results
were compared to ab initio calculations from the valence-space in-medium
similarity renormalization group, resulting in a good agreement.Comment: 7 pages, 3 figure
Properties of metastable alkaline-earth-metal atoms calculated using an accurate effective core potential
The first three electronically excited states in the alkaline-earth-metal
atoms magnesium, calcium, and strontium comprise the (nsnp) triplet P^o_J
(J=0,1,2) fine-structure manifold. All three states are metastable and are of
interest for optical atomic clocks as well as for cold-collision physics. An
efficient technique--based on a physically motivated potential that models the
presence of the ionic core--is employed to solve the Schroedinger equation for
the two-electron valence shell. In this way, radiative lifetimes, laser-induced
clock shifts, and long-range interaction parameters are calculated for
metastable Mg, Ca, and Sr.Comment: 13 pages, 9 table
Approximation Algorithms for Scheduling Parallel Jobs: Breaking the Approximation Ratio of 2
In this paper we study variants of the non-preemptive parallel job scheduling problem in which the number of machines is polynomially bounded in the number of jobs. For this problem we show that a schedule with length at most (1 + ε)OPT can be calculated in polynomial time. Unless P = NP, this is the best possible result (in the sense of approximation ratio), since the problem is strongly NP-hard. For the case, where all jobs must be allotted to a subset of consecutive machines, a schedule with length at most (1.5 + ε)OPT can be calculated in polynomial time. The previously best known results are algorithms with absolute approximation ratio 2. Furthermore, we extend both algorithms to the case of malleable jobs with the same approximation ratios
Decentralized subcontractor scheduling with divisible jobs
Subcontracting allows manufacturer agents to reduce completion times of their jobs and thus obtain savings. This paper addresses the coordination of decentralized scheduling systems with a single subcontractor and several agents having divisible jobs. Assuming complete information, we design parametric pricing schemes that strongly coordinate this decentralized system, i.e., the agents’ choices of subcontracting intervals always result in efficient schedules. The subcontractor’s revenue under the pricing schemes depends on a single parameter which can be chosen to make the revenue as close to the total savings as required. Also, we give a lower bound on the subcontractor’s revenue for any coordinating pricing scheme. Allowing private information about processing times, we prove that the pivotal mechanism is coordinating, i.e., agents are better off by reporting their true processing times, and by participating in the subcontracting. We show that the subcontractor’s maximum revenue with any coordinating mechanism under private information equals the lower bound of that with coordinating pricing schemes under complete information. Finally, we address the asymmetric case where agents obtain savings at different rates per unit reduction in completion times. We show that coordinating pricing schemes do not always exist in this case
High-precision QEC-value measurement of the superallowed β+ emitter 22Mg and an ab initio evaluation of the A = 22 isobaric triplet
A direct -value measurement of the superallowed emitter
Mg was performed using TRIUMF's Ion Trap for Atomic and Nuclear science
(TITAN). The direct ground-state to ground-state atomic mass difference between
Mg and Na was determined to be ~keV,
representing the most precise single measurement of this quantity to date. In a
continued push towards calculating superallowed isospin-symmetry-breaking (ISB)
corrections from first principles, ab-initio shell-model calculations of the
IMME are also presented for the first time using the valence-space
in-medium similarity renormalization group formalism. With particular starting
two- and three-nucleon forces, this approach demonstrates a level of agreement
with the experimental data that suggests reliable ab-initio calculations of
superallowed ISB corrections are now possible
Aging of the mammalian gastrointestinal tract: a complex organ system
Gastrointestinal disorders are a major cause of morbidity in the elderly population. The gastrointestinal tract is the most complex organ system; its diverse cells perform a range of functions essential to life, not only secretion, digestion, absorption and excretion, but also, very importantly, defence. The gastrointestinal tract acts not only as a barrier to harmful materials and pathogens but also contains the vast number of beneficial bacterial populations that make up the microbiota. Communication between the cells of the gastrointestinal tract and the central nervous and endocrine systems modifies behaviour; the organisms of the microbiota also contribute to this brain–gut–enteric microbiota axis. Age-related physiological changes in the gut are not only common, but also variable, and likely to be influenced by external factors as well as intrinsic aging of the cells involved. The cellular and molecular changes exhibited by the aging gut cells also vary. Aging intestinal smooth muscle cells exhibit a number of changes in the signalling pathways that regulate contraction. There is some evidence for age-associated degeneration of neurons and glia of the enteric nervous system, although enteric neuronal losses are likely not to be nearly as extensive as previously believed. Aging enteric neurons have been shown to exhibit a senescence-associated phenotype. Epithelial stem cells exhibit increased mitochondrial mutation in aging that affects their progeny in the mucosal epithelium. Changes to the microbiota and intestinal immune system during aging are likely to contribute to wider aging of the organism and are increasingly important areas of analysis. How changes of the different cell types of the gut during aging affect the numerous cellular interactions that are essential for normal gut functions will be important areas for future aging research
Sensing of Dietary Lipids by Enterocytes: A New Role for SR-BI/CLA-1
BACKGROUND: The intestine is responsible for absorbing dietary lipids and delivering them to the organism as triglyceride-rich lipoproteins (TRL). It is important to determine how this process is regulated in enterocytes, the absorptive cells of the intestine, as prolonged postprandial hypertriglyceridemia is a known risk factor for atherosclerosis. During the postprandial period, dietary lipids, mostly triglycerides (TG) hydrolyzed by pancreatic enzymes, are combined with bile products and reach the apical membrane of enterocytes as postprandial micelles (PPM). Our aim was to determine whether these micelles induce, in enterocytes, specific early cell signaling events that could control the processes leading to TRL secretion. METHODOLOGY/PRINCIPAL FINDINGS: The effects of supplying PPM to the apex of Caco-2/TC7 enterocytes were analyzed. Micelles devoid of TG hydrolysis products, like those present in the intestinal lumen in the interprandial period, were used as controls. The apical delivery of PPM specifically induced a number of cellular events that are not induced by interprandial micelles. These early events included the trafficking of apolipoprotein B, a structural component of TRL, from apical towards secretory domains, and the rapid, dose-dependent activation of ERK and p38MAPK. PPM supply induced the scavenger receptor SR-BI/CLA-1 to cluster at the apical brush border membrane and to move from non-raft to raft domains. Competition, inhibition or knockdown of SR-BI/CLA-1 impaired the PPM-dependent apoB trafficking and ERK activation. CONCLUSIONS/SIGNIFICANCE: These results are the first evidence that enterocytes specifically sense postprandial dietary lipid-containing micelles. SR-BI/CLA-1 is involved in this process and could be a target for further study with a view to modifying intestinal TRL secretion early in the control pathway
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