924 research outputs found
The infimum, supremum and geodesic length of a braid conjugacy class
Algorithmic solutions to the conjugacy problem in the braid groups B_n were
given by Elrifai-Morton in 1994 and by the authors in 1998. Both solutions
yield two conjugacy class invariants which are known as `inf' and `sup'. A
problem which was left unsolved in both papers was the number m of times one
must `cycle' (resp. `decycle') in order to increase inf (resp. decrease sup) or
to be sure that it is already maximal (resp. minimal) for the given conjugacy
class. Our main result is to prove that m is bounded above by n-2 in the
situation of the second algorithm and by ((n^2-n)/2)-1 in the situation of the
first. As a corollary, we show that the computation of inf and sup is
polynomial in both word length and braid index, in both algorithms. The
integers inf and sup determine (but are not determined by) the shortest
geodesic length for elements in a conjugacy class, as defined by Charney, and
so we also obtain a polynomial-time algorithm for computing this geodesic
length.Comment: 15 pages. Journa
EFFECTS OF TEMPERING AND PWHT ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF SA508 GR.4N STEEL
Presented in this study are the variations of microstructures and mechanical properties with tempering and Post-Weld Heat Treatment (PWHT) conditions for SA508 Gr.4N steel used as Reactor Pressure Vessel (RPV) material. The blocks of model alloy were austenitized at the conventional temperature of 880 °C, then tempered and post-weld heat treated at four different conditions. The hardness and yield strength decrease with increased tempering and PWHT temperatures, but impact toughness is significantly improved, especially in the specimens tempered at 630 °C. The sample tempered at 630 °C with PWHT at 610 °C shows optimum mechanical properties in hardness, strength, and toughness, excluding only the transition property in the low temperature region. The microstructural observation and quantitative analysis of carbide size distribution show that the variations of mechanical properties are caused by the under-tempering and carbide coarsening which occurred during the heat treatment process. The introduction of PWHT results in the deterioration of the ductile-brittle transition property by an increase of coarse carbides controlling cleavage initiation, especially in the tempered state at 630 °C
High density of ice krill (Euphausia crystallorophias) in the Amundsen sea coastal polynya, Antarctica
High densities of ice krill Euphausia crystallorophias were observed along six acoustic transects within the Amundsen Sea Coastal Polynya, Antarctica. Two-frequency acoustic backscatter data was examined in the austral summers of January 2011 and February 2012. A dB identification window (Sv120−38) identified ice krill dominating the acoustic backscatter. The density of ice krill, calculated with the stochastic distorted-wave born approximation model, ranged between 4.5 and 30 g wet mass m−2 for each transect (a mean of 16 g wet mass m−2 for all transects), these high values are an order of magnitude higher than recorded previously in the Ross Sea Polynya. High densities were detected along the ice shelf and near the boundary between pack ice and coastal polynya, and we postulate that these could be important habitats for ice krill. The high densities observed along the transects make ice krill a potentially important, but poorly known contributor to these high-latitude shelf food webs
Automatic 3D Registration of Dental CBCT and Face Scan Data using 2D Projection images
This paper presents a fully automatic registration method of dental cone-beam
computed tomography (CBCT) and face scan data. It can be used for a digital
platform of 3D jaw-teeth-face models in a variety of applications, including 3D
digital treatment planning and orthognathic surgery. Difficulties in accurately
merging facial scans and CBCT images are due to the different image acquisition
methods and limited area of correspondence between the two facial surfaces. In
addition, it is difficult to use machine learning techniques because they use
face-related 3D medical data with radiation exposure, which are difficult to
obtain for training. The proposed method addresses these problems by reusing an
existing machine-learning-based 2D landmark detection algorithm in an
open-source library and developing a novel mathematical algorithm that
identifies paired 3D landmarks from knowledge of the corresponding 2D
landmarks. A main contribution of this study is that the proposed method does
not require annotated training data of facial landmarks because it uses a
pre-trained facial landmark detection algorithm that is known to be robust and
generalized to various 2D face image models. Note that this reduces a 3D
landmark detection problem to a 2D problem of identifying the corresponding
landmarks on two 2D projection images generated from two different projection
angles. Here, the 3D landmarks for registration were selected from the
sub-surfaces with the least geometric change under the CBCT and face scan
environments. For the final fine-tuning of the registration, the Iterative
Closest Point method was applied, which utilizes geometrical information around
the 3D landmarks. The experimental results show that the proposed method
achieved an averaged surface distance error of 0.74 mm for three pairs of CBCT
and face scan datasets.Comment: 8 pages, 6 figures, 2 table
Replication of the genetic effects of IFN regulatory factor 5 (IRF5) on systemic lupus erythematosus in a Korean population
Recently, two studies provided convincing evidence that IFN regulatory factor 5 (IRF5) gene polymorphisms are significantly associated with systemic lupus erythematosus (SLE) in several white populations. To replicate the association with SLE in an Asian population, we examined the genetic effects in our SLE cohort from a Korean population. A total of 1,565 subjects, composed of 593 cases and 972 controls, were genotyped using the TaqMan® (Applied Biosystems, Foster City, CA, USA) method. The genetic effects of polymorphisms on the risk of SLE were evaluated using χ2 tests and a Mantel–Haenszel meta-analysis. Statistical analysis revealed results in the Korean population were similar to the previous reports from white populations. The rs2004640 T allele had a higher frequency in SLE cases (0.385) than controls (0.321; odds ratio (OR) = 1.32, P = 0.0003). In combined analysis, including all seven independent cohorts from the three studies so far, robust and consistent associations of the rs2004640 T allele with SLE were observed. The estimate of risk was OR = 1.44 (range, 1.34–1.55), with an overall P = 1.85 × 10-23 for the rs2004640 T allele. The haplotype (rs2004640T–rs2280714T) involved in both the alternative splice donor site and the elevated expression of IRF5 also had a highly significant association with SLE (pooled, P = 2.11 × 10-16). Our results indicate that the genetic effect on the risk of SLE mediated by IRF5 variants can be generally accepted in both white and Asian populations
Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor
We have explored a new mechanism for switching magnetism and
superconductivity in a magnetically frustrated iron-based superconductor using
spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single
crystal SrVOFeAs shows that a spin-polarized tunneling current can
switch the Fe-layer magnetism into a non-trivial (22) order, not
achievable by thermal excitation with unpolarized current. Our tunneling
spectroscopy study shows that the induced (22) order has
characteristics of plaquette antiferromagnetic order in Fe layer and strongly
suppressed superconductivity. Also, thermal agitation beyond the bulk Fe spin
ordering temperature erases the state. These results suggest a new
possibility of switching local superconductivity by changing the symmetry of
magnetic order with spin-polarized and unpolarized tunneling currents in
iron-based superconductors.Comment: 33 pages, 16 figure
Severe ARDS caused by adenovirus: early initiation of ECMO plus continuous renal replacement therapy
Use of Nafamostat Mesilate as an Anticoagulant during Extracorporeal Membrane Oxygenation
Although the incidence of bleeding complications during extracorporeal membrane oxygenator (ECMO) support has decreased in various trials, bleeding is still the most fatal complication. We investigated the ideal dosage and efficacy of nafamostat mesilate for use with ECMO in patients with acute cardiac or respiratory failure. We assessed 73 consecutive patients who received ECMO due to acute cardiac or respiratory failure between January 2006 and December 2009. To evaluate the efficacy of nafamostat mesilate, we divided the patients into 2 groups according to the anticoagulants used during ECMO support. All patients of nafamostat mesilate group were male with a mean age of 49.2 yr. Six, 3, 5, and 3 patients were diagnosed with acute myocardial infarction, cardiac arrest, septic shock, and acute respiratory distress syndrome, respectively. The mean dosage of nafamostat mesilate was 0.64 mg/kg/hr, and the mean duration of ECMO was 270.7 hr. The daily volume of transfused packed red blood cells, fresh frozen plasma, and cryoprecipitate and the number of complications related to hemorrhage and thrombosis was lower in the nafamostat mesilate group than in the heparin group. Nafamostat mesilate should be considered as an alternative anticoagulant to heparin to reduce bleeding complications during ECMO
Permanent Pacemaker for Syncope after Heart Transplantation with Bicaval Technique
Sinus node dysfunction occurs occasionally after heart transplantation and may be caused by surgical trauma, ischemia to the sinus node, rejection, drug therapy, and increasing donor age. However, the timing and indication of permanent pacemaker insertion due to sinus node dysfunction following heart transplantation is contentious. Here, we report a case of a permanent pacemaker insertion for syncope due to sinus arrest after heart transplantation, even with a bicaval technique, which has been known to associate with few incidences of sinus node dysfunction
Case Report Jejunogastric intussusception: a rare complication of gastric cancer surgery
Abstract: Jejunogastric intussusception (JGI) is a rare condition and less than 200 cases have been published since its first description in 1914. In addition, JGI is potentially lethal complication of gastrectomy or gastrojejunostomy. We report the case of a 73-year-old man with a history of a Billroth II procedure who presented to the emergency department after 6 hours of epigastric pain and hematemesis. Endoscopy and computed tomography showed intussuscepted jejunum through a gastrojejunostomy that required emergency operation. At laparotomy a retrograde type II, JGI was confirmed and managed by resection of involved intestine. Postoperative recovery was uneventful. This case presents the rare complication of acute jejunogastric intussusception more than 25 years after a Billroth II procedure
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