Unconventional pairing in bipolaronic theories

Various mechanisms have been put forward for cuprate superconductivity, which fit largely into two camps: spin-fluctuation and electron-phonon (el-ph) mechanisms. However, in spite of a large effort, electron-phonon interactions are not fully understood away from clearly defined limits. To this end, we use a numerically exact algorithm to simulate the binding of bipolarons. We present the results of a continuous-time quantum Monte-Carlo (CTQMC) algorithm on a tight-binding lattice, for bipolarons with arbitrary interaction range in the presence of strong coulomb repulsion. The algorithm is sufficiently efficient that we can discuss properties of bipolarons with various pairing symmetries. We investigate the effective mass and binding energies of singlet and triplet real-space bipolarons for the first time, and discuss the extensions necessary to investigate $d$-symmetric pairs.Comment: Submitted to M2S-HTSC VIII, Dresden 2006, 2 page

Effects of lattice geometry and interaction range on polaron dynamics

We study the effects of lattice type on polaron dynamics using a continuous-time quantum Monte-Carlo approach. Holstein and screened Froehlich polarons are simulated on a number of different Bravais lattices. The effective mass, isotope coefficients, ground state energy and energy spectra, phonon numbers, and density of states are calculated. In addition, the results are compared with weak and strong coupling perturbation theory. For the Holstein polaron, it is found that the crossover between weak and strong coupling results becomes sharper as the coordination number is increased. In higher dimensions, polarons are much less mobile at strong coupling, with more phonons contributing to the polaron. The total energy decreases monotonically with coupling. Spectral properties of the polaron depend on the lattice type considered, with the dimensionality contributing to the shape and the coordination number to the bandwidth. As the range of the electron-phonon interaction is increased, the coordination number becomes less important, with the dimensionality taking the leading role.Comment: 16 pages, 12 figure

Cross-Layer Design for Green Power Control

In this work, we propose a new energy efficiency metric which allows one to optimize the performance of a wireless system through a novel power control mechanism. The proposed metric possesses two important features. First, it considers the whole power of the terminal and not just the radiated power. Second, it can account for the limited buffer memory of transmitters which store arriving packets as a queue and transmit them with a success rate that is determined by the transmit power and channel conditions. Remarkably, this metric is shown to have attractive properties such as quasi-concavity with respect to the transmit power and a unique maximum, allowing to derive an optimal power control scheme. Based on analytical and numerical results, the influence of the packet arrival rate, the size of the queue, and the constraints in terms of quality of service are studied. Simulations show that the proposed cross-layer approach of power control may lead to significant gains in terms of transmit power compared to a physical layer approach of green communications.Comment: Presented in ICC 201

X-ray diffraction study of the crystal structure of the π-molecular compound pyrene···pyromellitic dianhydride at 19 K

The crystal structure of the pyrene···pyromellitic dianhydride (PMDA) π-molecular compound [(C _(16)H_(10):C_(10)-H_2O_6); PYRPMA] has been refined from intensities measured at 19 K using the low-temperature accessory designed by Samson, Goldish & Dick [J. Appl. Cryst. (1980), 13, 425-432] for a four-circle diffractometer. Earlier results for the ordered structure [Herbstein & Snyman (1969). Philos. Trans. R. Soc. London Ser. A, 264, 635-666] are confirmed and extended; at 19 K, a = 13.664 (3), b = 9.281 (2), c = 14.420 (3) Å, β = 91.80 (2)°, space group P2_1/n = 4, with two sets of pyrenes at independent centres of symmetry and the four PMDAs at general positions. The geometrical structures of the two components are in good agreement with quantum mechanical calculations. Analyses of thermal motion and packing show that one set of pyrenes is more tightly packed than the other; the principal interactions in the crystal are π-π* plane-to-plane interactions between pyrene and PMDA and >CH···O=C<, between pyrene and PMDA, and between PMDAs

Age grading \u3cem\u3eAn. gambiae\u3c/em\u3e and \u3cem\u3eAn. arabiensis\u3c/em\u3e using near infrared spectra and artificial neural networks

Background Near infrared spectroscopy (NIRS) is currently complementing techniques to age-grade mosquitoes. NIRS classifies lab-reared and semi-field raised mosquitoes into \u3c or ≥ 7 days old with an average accuracy of 80%, achieved by training a regression model using partial least squares (PLS) and interpreted as a binary classifier. Methods and findings We explore whether using an artificial neural network (ANN) analysis instead of PLS regression improves the current accuracy of NIRS models for age-grading malaria transmitting mosquitoes. We also explore if directly training a binary classifier instead of training a regression model and interpreting it as a binary classifier improves the accuracy. A total of 786 and 870 NIR spectra collected from laboratory reared An. gambiae and An. arabiensis, respectively, were used and pre-processed according to previously published protocols. The ANN regression model scored root mean squared error (RMSE) of 1.6 ± 0.2 for An. gambiae and 2.8 ± 0.2 for An. arabiensis; whereas the PLS regression model scored RMSE of 3.7 ± 0.2 for An. gambiae, and 4.5 ± 0.1 for An. arabiensis. When we interpreted regression models as binary classifiers, the accuracy of the ANN regression model was 93.7 ± 1.0% for An. gambiae, and 90.2 ± 1.7% for An. arabiensis; while PLS regression model scored the accuracy of 83.9 ± 2.3% for An. gambiae, and 80.3 ± 2.1% for An. arabiensis. We also find that a directly trained binary classifier yields higher age estimation accuracy than a regression model interpreted as a binary classifier. A directly trained ANN binary classifier scored an accuracy of 99.4 ± 1.0 for An. gambiae and 99.0 ± 0.6% for An. arabiensis; while a directly trained PLS binary classifier scored 93.6 ± 1.2% for An. gambiae and 88.7 ± 1.1% for An. arabiensis. We further tested the reproducibility of these results on different independent mosquito datasets. ANNs scored higher estimation accuracies than when the same age models are trained using PLS. Regardless of the model architecture, directly trained binary classifiers scored higher accuracies on classifying age of mosquitoes than regression models translated as binary classifiers. Conclusion We recommend training models to estimate age of An. arabiensis and An. gambiae using ANN model architectures (especially for datasets with at least 70 mosquitoes per age group) and direct training of binary classifier instead of training a regression model and interpreting it as a binary classifier

Quantification of anterior translation of tibia over femur using Lachmeter in anterior cruciate ligament reconstruction with hamstring tendon autograft

Background: The anterior cruciate ligament (ACL) is an important restraint on anterior tibial translation of the knee. Arthroscopic ACL reconstruction using hamstring tendon autograft is the most widely accepted surgical procedure for ACL insufficiency. This study is assessing the effect of ACL reconstruction by hamstring tendon autograft on the anteroposterior stability of the knee joint by measuring the side-to-side difference of anterior tibial translation using the Lachmeter. We are also assessing the functional outcome of the same surgery using international knee documentation committee (IKDC) score. Methods: The study included 30 patients who were admitted for ACL reconstruction with hamstring tendon autograft. The side-to-side difference of anterior tibial translation was assessed by using Lachmeter preoperatively and postoperatively at the end of the 1st, 3rd, and 6th months. The IKDC score was assessed preoperatively and postoperatively at the end of 6th month. Results: The mean Lachmeter value of respondents in the current study was 4.31±0.56 mm during the preoperative period. Lachmeter values were 2.79±0.42 mm, 2.09±0.42 mm, and 1.29±0.39 mm, respectively, at the end of the first, third, and sixth months postoperatively. Mean preoperative and postoperative 6th month IKDC scores were 55.83±7.7 and 89.20±5.3 respectively. Conclusions: There is significant serial improvement in the side-to-side difference of anterior tibial translation in the 6 months of post operative period following ACL reconstruction using hamstring tendon autograft. The improved IKDC score from preoperative to postoperative level is also indicating a positive functional outcome

Comparison of effectiveness of intraoperative subperiosteal versus periarticular analgesic cocktail injection for post operative analgesia in patients undergoing total knee arthroplasty

Background: Early postoperative pain management is pivotal in patients undergoing Total knee arthroplasty. The advantage of Local infiltration analgesia is its ability to provide control of pain without interfering with motor strength of the lower extremity, thereby allowing early mobilization of patients. This study compares the effectiveness of local analgesic cocktail injection given through subperiosteal vs. periarticular routes. Methods: The study included 30 patients admitted for primary total knee arthroplasty. They were grouped into two groups based on different injection sites. Group A included patients who received subperiosteal injection and Group B included patients who received periarticular injection, under spinal anaesthesia. The difference in pain among the two groups, using VAS at 12, 24, 48, and 72 hrs postoperatively, postoperative range of movements, and Functional outcome using IKDC score at the end of 6 months were assessed and compared between the two groups. Results: The mean VAS scores at 12, 24, 48, and 72 hrs were 0.87±0.35, 1.47±0.52, 1.80±0.41, 1.07±0.46 in subperiosteal group and 2.00±0.53, 2.47±0.52, 2.80±0.56, 1.93±0.59 in periarticular group. The 6 months postoperative IKDC scores were 51.34±0.41 and 51.04±0.61 respectively. Conclusions: Subperiosteal cocktail injection can significantly reduce the postoperative pain and result in early recovery of range of movements, compared with periarticular cocktail injection in patients undergoing Total knee arthroplasty. But the long-term functional outcomes were comparable among both the groups

Observation of vortex dipoles in an oblate Bose-Einstein condensate

We report experimental observations and numerical simulations of the formation, dynamics, and lifetimes of single and multiply charged quantized vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing superfluid flow around a repulsive gaussian obstacle within the BEC. By controlling the flow velocity we determine the critical velocity for the nucleation of a single vortex dipole, with excellent agreement between experimental and numerical results. We present measurements of vortex dipole dynamics, finding that the vortex cores of opposite charge can exist for many seconds and that annihilation is inhibited in our highly oblate trap geometry. For sufficiently rapid flow velocities we find that clusters of like-charge vortices aggregate into long-lived dipolar flow structures.Comment: 4 pages, 4 figures, 1 EPAPS fil