Luttinger liquid superlattices: realization of gapless insulating phases

We investigate Luttinger Liquid superlattices, a periodic structure composed of two kinds of one-dimensional systems of interacting electrons. We calculate several properties of the low-energy sector: the effective charge and spin velocities, the compressibility, various correlation functions, the Landauer conductance and the Drude weight. The low-energy properties are subsumed into effective parameters, much like homogeneous one-dimensional systems. A generic result is the weighted average nature of these parameters, in proportion to the spatial extent of the underlying subunits, pointing to the possibility of ``engineered'' structures. As a specific realization, we consider a one-dimensional Hubbard superlattice, which consists of a periodic arrangement of two long Hubbard chains with different coupling constants and different hopping amplitudes. This system exhibits a rich phase diagram with several phases, both metallic and insulating. We have found that gapless insulating phases are present over a wide range of parameters.Comment: 16 pages, 15 figures, RevTeX

Improved wear performance of ultra high molecular weight polyethylene coated with hydrogenated diamond like carbon

Hydrogenated diamond like carbon (DLCH) thin films were deposited on medical grade ultra high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition. The DLCH coating thicknesses ranged from 250 to 700. nm. The substrates were disks made of UHMWPEs typically used for soft components in artificial joints, namely virgin GUR 1050 and highly crosslinked (gamma irradiated in air to 100. kGy) UHMWPEs. Mechanical and tribological properties under bovine serum lubrication at body temperature were assessed on coated and uncoated polyethylenes by means of nano-hardness and ball-on-disk tests, respectively. Morphological features of the worn surfaces were obtained by confocal microscopy and scanning electron microscopy. This study confirms an increase in surface hardness and good wear resistance for coated materials after 24. h of sliding test compared to uncoated polyethylene. These results point out that to coat UHMWPE with DLCH films could be a potential method to reduce backside wear in total hip and knee arthroplasties.Ministerio de Ciencia y Educación MAT2006-12603- C02-01, CSD2008-0002

SATISFACCIÓN LABORAL PARA EL CAMBIO EN EL NUEVO ESCENARIO MUNDIAL: ESTUDIO DE EMPRESA MAQUILADORA UBICADA EN EL SURESTE DE MÉXICO

Esta investigación tiene como objetivo determinar el grado de satisfacción laboral del personal de una empresa maquiladora ubicada en el sureste de México, específicamente en el Estado de Campeche. La mejora de la maquiladora en estudio necesita superar no sólo los obstáculos económicos y técnicos, sino también, aquellos relacionados con la satisfacción de sus trabajadores, la cual puede estar afectando problemas de desarrollo, productividad y competitividad de la misma. Este estudio es exploratorio y descriptivo, primero se realizó una medición cuantitativa y posteriormente se aplicaron entrevistas cualitativas. Los resultados indican que el personal de la maquiladora se encuentra muy satisfecho con las escalas: seguridad, utilización de habilidades, y logro. Por otra parte, se encontró poca satisfacción con las escalas: independencia, variedad, y creatividad. Con relación a la satisfacción en general, el resultado fue que el personal se encuentra satisfecho. El motivo de esta satisfacción se debe principalmente al programa de estímulos y recompensas por incrementos en los niveles de productividad. A pesar de estar satisfechos, los trabajadores perciben que las relaciones con sus jefes se dan muy poco. Además, sienten que los tiene muy vigilados pues lo único que les interesa a los gerentes es la productividad, que el trabajo salga adelante y que generen utilidades. Por tanto, -ante un mundo globalizado caracterizado por el utilitarismo económico- se sugiere que los gerentes de la maquiladora tomen en cuenta también otros factores que influyen en el comportamiento de los trabajadores, tales como las buenas relaciones humanas y sociales de tal forma que hagan sentir importantes a los trabajadores en beneficio de la maquiladora y de la localidad

Charge-density waves in one-dimensional Hubbard superlattices

We study the formation of charge density waves (CDW's) in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive (U>0) and free (U=0) sites. By means of Lanczos diagonalizations for the ground state, we calculate the charge structure factor. Our results show that while the superlattice structure affects the modulation of the charge density waves, the periodicity can still be predicted through an effective density. We also show that, for a fixed repulsive layer thickness, the periodicity of the CDW is an oscillatory function of the free layer thickness.Comment: 4 pages, 4 figure

Luttinger liquid superlattices

We calculate the correlation functions and the DC conductivity of Luttinger liquid superlattices, modeled by a repeated pattern of interacting and free Luttinger liquids. In a specific realization, where the interacting subsystem is a Hubbard chain, the system exhibits a rich phase diagram with four different phases: two metals and two compressible insulators. In general, we find that the effective low energy description amalgamates features of both types of liquids in proportion to their spatial extent, suggesting the interesting possibility of `engineered' Luttinger liquids.Comment: RevTeX, 5 pages, 3 figure

(4-Hydr­oxy-2,5-dimethyl­phen­yl)phenyl­methanone

The title compound, C15H14O2, was obtained by Friedel–Crafts acyl­ation between 2,5-dimethyl­phenol and benzoyl chloride in the presence of aluminium chloride as a catalyst. The dihedral angle between the benzene rings is 61.95 (4)°. In the crystal, O—H⋯O hydrogen bonding and C—H⋯O weak inter­actions lead to polymeric C(6), C(8) and C(11) chains along the a, b and c-axis directions, respectively

Quantifying Potential Cost-Savings Through an Alternative Imaging-Based Diagnostic Process in Presumptive Seronegative Rheumatoid Arthritis

Background: Seronegative rheumatoid arthritis (SRA) is a condition that is not well understood and difficult to confirm by a conventional diagnostic process. We aimed to quantify the potential cost-savings of an alternative diagnostic process (ADP) imaging-based, for patients with presumptive SRA from everyday clinical practice. Methods: We performed a retrospective analysis for patients with presumptive SRA who tested negative for both rheumatoid factor and anti-cyclic citrullinated peptide antibodies, through an ADP imaging-based, that is a standard clinical practice in our center. After we confirmed the diagnosis of SRA or reclassified patients in terms of another proper diagnosis, we estimate direct costs in two scenarios: a conventional and ADP. We compared the cost of RA treatment during the first year against the cost of the most misdiagnosed treatment (osteoarthritis) found after applying the ADP to determine potential cost-savings. Results: We included 440 patients with a presumptive diagnosis of SRA. According to the imaging-based ADP, SRA was confirmed in 106/440 (24.1%), unspecified RA in 9/440 (2.0%), and osteoarthritis in 325/440 (73.9%) of those patients. Although the costs of conventional diagnosis per patient is lower than those of ADP ($59,20 USD vs$269,57 USD), we found a potential drug cost-savings of $1,570,775.20 US Dollars after 1 year of correct treatment. Conclusion: An alternative diagnosis process, including X-rays, US and MRI imaging, and clinical and blood-test assessment, not only increased diagnostic certainty in patients referred for evaluation of presumptive SRA but also suggested a potential cost-savings in pharmacological treatments avoided in misdiagnosed patients

Interrelationship between different loads in resisted sprints, half-squat 1RM, and kinematic variables in trained athletes

Resisted sprint running is a common training method for improving sprint-specific strength. It is well-known that an athlete's time to complete a sled-towing sprint increases linearly with increasing sled load. However, to our knowledge, the relationship between the maximum load in sled-towing sprint and the sprint time is unknown, The main purpose of this research was to analyze the relationship between the maximum load in sled-towing sprint, half-squat maximal dynamic strength and the velocity in the acceleration phase in 20-m sprint. A second aim was to compare sprint performance when athletes ran under different conditions: un-resisted and towing sleds. Twenty-one participants (17.86±2.27 years; 1.77±0.06 m and 69.24±7.20 kg) completed a one repetition maximum test (1 RM) from a half-squat position (159.68±22.61 kg) and a series of sled-towing sprints with loads of 0, 5, 10, 15, 20, 25, 30% body mass (Bm) and the maximum resisted sprint load. No significant correlation (P<0.05) was found between half-squat 1 RM and the sprint time in different loaded conditions. Conversely, significant correlations (P<0.05) were found between maximum load in resisted sprint and sprint time (20-m sprint time, r=−0.71; 5% Bm, r=−0.73; 10% Bm, r=−0.53; 15% Bm, r=−0.55; 20% Bm, r=−0.65; 25% Bm, r=−0.44; 30% Bm, r=−0.63; MaxLoad, r= 0.93). The sprinting velocity significantly decreased by 4–22% with all load increases. Stride length (SL) also decreased (17%) significantly across all resisted conditions. In addition, there were significant differences in stride frequency (SF) with loads over 15% Bm. It could be concluded thatthe knowledge of the individual maximal load in resisted sprint and the effects on the sprinting kinematic with different loads, could be interesting to determinate the optimal load to improve the acceleration phase at sprint running.Actividad Física y Deport