Stabilizing quantum metastable states in a time-periodic potential

Metastability of a particle trapped in a well with a time-periodically oscillating barrier is studied in the Floquet formalism. It is shown that the oscillating barrier causes the system to decay faster in general. However, avoided crossings of metastable states can occur with the less stable states crossing over to the more stable ones. If in the static well there exists a bound state, then it is possible to stabilize a metastable state by adiabatically increasing the oscillating frequency of the barrier so that the unstable state eventually cross-over to the stable bound state. It is also found that increasing the amplitude of the oscillating field may change a direct crossing of states into an avoided one.Comment: 7 pages, 6 figure

Low Catalyst Loadings in Olefin Metathesis: Synthesis of Nitrogen Heterocycles by Ring-Closing Metathesis

A series of ruthenium catalysts have been screened under ring-closing metathesis (RCM) conditions to produce five-, six-, and seven-membered carbamate-protected cyclic amines. Many of these catalysts demonstrated excellent RCM activity and yields with as low as 500 ppm catalyst loadings. RCM of the five-membered carbamate series could be run neat, the six-membered carbamate series could be run at 1.0 M, and the seven-membered carbamate series worked best at 0.2−0.05 M

Quantum metastability in a class of moving potentials

In this paper we consider quantum metastability in a class of moving potentials introduced by Berry and Klein. Potential in this class has its height and width scaled in a specific way so that it can be transformed into a stationary one. In deriving the non-decay probability of the system, we argue that the appropriate technique to use is the less known method of scattering states. This method is illustrated through two examples, namely, a moving delta-potential and a moving barrier potential. For expanding potentials, one finds that a small but finite non-decay probability persists at large times. Generalization to scaling potentials of arbitrary shape is briefly indicated.Comment: 10 pages, 1 figure

Fluoroscopically guided anterior atlantoaxial transarticular screws: a feasibility and trajectory study using CT-based simulation software

Background context : Anterior transarticular screw (ATAS) fixation has been suggested as a viable alternative to posterior stabilization. However, we are not aware of previous reports attempting to establish the usefulness of specific fluoroscopic landmark-guided trajectories in the use of ATAS, and we could find no reference to it in a computerized search using MEDLINE. Purpose : To determine the anatomic feasibility of ATAS placement using defined fluoroscopic landmarks to guide screw trajectory. Study design : Evaluation using three-dimensional screw insertion simulation software and 1.0-mm-interval computed tomographic scans. Patient sample : Computed tomographic scans of 100 patients including 50 men and 50 women. Outcome measures : Incidence of violation of the vertebral artery groove of C1 and C2, the spinal canal, and the atlanto-occipital joint and screw lengths and lengths of C1 and C2 purchase. Methods : Four screw trajectories were determined: promontory screw (PS), single central facet (CF) screw, and medial (MF) and lateral (LF) double facet screws. Placement of a 4.0-mm screw was simulated using defined fluoroscopic landmarks for each trajectory. The previously mentioned outcome measures were evaluated and compared for the four trajectories. This study was not supported by any financial sources, and there is no topic-specific potential conflict of interest with this study. Results : No violation of the C1 or C2 vertebral artery groove or of the spinal canal was observed for any of the screw types. Screw lengths and the length of C2 purchase were by far the longest for PS (40.4 +/- 2.8 and 25.7 +/- 2.1 mm, respectively; p < .001 in all post hoc comparisons). The length of C1 purchase was longer for CF (16.4 +/- 2.3 mm) and LF (15.8 +/- 1.6 mm) than PS (14.7 +/- 2.0 mm) and MF (14.6 +/- 2.4 mm) (p <= .001, respectively). There was no atlanto-occipital joint violation if the length of C1 purchase was set at 12 mm for CF and LF and at 10 mm for PS and MF. Conclusions : Our results suggest that it may be possible to place ATASs without violating the vertebral artery groove, spinal canal, or the atlanto-occipital joint by using the described entry points, trajectories, and fluoroscopic landmarks.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000004226/16SEQ:16PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000004226ADJUST_YN:YEMP_ID:A079510DEPT_CD:801CITE_RATE:3.355FILENAME:e058t_padua_fluoroscopically guided anterior atlantoaxial transarticular screws.pdfDEPT_NM:의학과EMAIL:[email protected]_YN:YCONFIRM:

Stroke Factors Associated with Thrombolysis Use in Hospitals in Singapore and US: A Cross-Registry Comparative Study

Background and Objectives: This paper aims to describe and compare the characteristics of 2 stroke populations in Singapore and in St. Louis, USA, and to document thrombolysis rates and contrast factors associated with its uptake in both populations. Methods: The stroke populations described were from the Singapore Stroke Registry (SSR) in -Singapore and the Cognitive Rehabilitation Research Group Stroke Registry (CRRGSR) in St. Louis, MO, USA. The registries were compared in terms of demographics and stroke risk factor history. Logistic regression was used to determine factors associated with thrombolysis uptake. Results: A total of 39,323 and 8,106 episodes were recorded in SSR and CRRGSR, respectively, from 2005 to 2012. Compared to CRRGSR, patients in SSR were older, male, and from the ethnic majority. Thrombolysis rates in SSR and CRRGSR were 2.5 and 8.2%, respectively, for the study period. History of ischemic heart disease or atrial fibrillation was associated with increased uptake in both populations, while history of stroke was associated with lower uptake. For SSR, younger age and males were associated with increased uptake, while having a history of smoking or diabetes was associated with decreased uptake. For CRRGSR, ethnic minority status was associated with decreased uptake. Conclusions: The comparison of stroke populations in Singapore and St Louis revealed distinct differences in clinicodemographics of the 2 groups. Thrombolysis uptake was driven by nonethnicity demographics in Singapore. Ethnicity was the only demographic driver of uptake in the CRRGSR population, highlighting the need to target ethnic minorities in increasing access to thrombolysis

Large scale enzyme based xenobiotic identification for exposomics.

Advances in genomics have revealed many of the genetic underpinnings of human disease, but exposomics methods are currently inadequate to obtain a similar level of understanding of environmental contributions to human disease. Exposomics methods are limited by low abundance of xenobiotic metabolites and lack of authentic standards, which precludes identification using solely mass spectrometry-based criteria. Here, we develop and validate a method for enzymatic generation of xenobiotic metabolites for use with high-resolution mass spectrometry (HRMS) for chemical identification. Generated xenobiotic metabolites were used to confirm identities of respective metabolites in mice and human samples based upon accurate mass, retention time and co-occurrence with related xenobiotic metabolites. The results establish a generally applicable enzyme-based identification (EBI) for mass spectrometry identification of xenobiotic metabolites and could complement existing criteria for chemical identification

Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws.

BACKGROUND CONTEXT: To our knowledge, no large series comparing the risk of vertebral artery injury by C1-C2 transarticular screw versus C2 pedicle screw have been published. In addition, no comparative studies have been performed on those with a high-riding vertebral artery and/or a narrow pedicle who are thought to be at higher risk than those with normal anatomy.PURPOSE: To compare the risk of vertebral artery injury by C1-C2 transarticular screw versus C2 pedicle screw in an overall patient population and subsets of patients with a high-riding vertebral artery and a narrow pedicle using computed tomography (CT) scan images and three-dimensional (3D) screw trajectory software.STUDY DESIGN: Radiographic analysis using CT scans.PATIENT SAMPLE: Computed tomography scans of 269 consecutive patients, for a total of 538 potential screw insertion sites for each type of screw.OUTCOME MEASURES: Cortical perforation into the vertebral artery groove of C2 by a screw.METHODS: We simulated the placement of 4.0 mm transarticular and pedicle screws using 1-mm-sliced CT scans and 3D screw trajectory software. We then compared the frequency of C2 vertebral artery groove violation by the two different fixation methods. This was done in the overall patient population, in the subset of those with a high-riding vertebral artery (defined as an isthmus height ≤5 mm or internal height ≤2 mm on sagittal images) and with a narrow pedicle (defined as a pedicle width ≤4 mm on axial images).RESULTS: There were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%). Most (82%) of the narrow pedicles had a concurrent high-riding vertebral artery, whereas only 54% of the high-riding vertebral arteries had a concurrent narrow pedicle. Overall, 9.5% of transarticular and 8.0% of pedicle screws violated the C2 vertebral artery groove without a significant difference between the two types of screws (p=.17). Among those with a high-riding vertebral artery, vertebral artery groove violation was significantly lower (p=.02) with pedicle (49%) than with transarticular (63%) screws. Among those with a narrow pedicle, vertebral artery groove violation was high in both groups (71% with transarticular and 76% with pedicle screws) but without a significant difference between the two groups (p=.55).CONCLUSIONS: Overall, neither technique has more inherent anatomic risk of vertebral artery injury. However, in the presence of a high-riding vertebral artery, placement of a pedicle screw is significantly safer than the placement of a transarticular screw. Narrow pedicles, which might be anticipated to lead to higher risk for a pedicle screw than a transarticular screw, did not result in a significant difference because most patients (82%) with narrow pedicles had a concurrent high-riding vertebral artery that also increased the risk with a transarticular screw. Except in case of a high-riding vertebral artery, our results suggest that the surgeon can opt for either technique and expect similar anatomic risks of vertebral artery injury.This study was supported by a Research Grant (04-2008-006) of Seoul National University Bundang Hospital of JSY (04-2008-006) with US $9,000.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000004226/9SEQ:9PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000004226ADJUST_YN:NEMP_ID:A076317DEPT_CD:801CITE_RATE:3.29FILENAME:e051t_tsj-2013_yeom_risk of vertebral artery injury_comparison between c1-c2 transarticular.pdfDEPT_NM:의학과EMAIL:[email protected]_YN:YCONFIRM:

Postoperative occipital neuralgia with and without C2 nerve root transection during atlantoaxial screw fixation: a post-hoc comparative outcome study of prospectively collected data

BACKGROUND CONTEXT:Although routine transection of the C2 nerve root during atlantoaxial segmental screw fixation has been recommended by some surgeons, it remains controversial and to our knowledge no comparative studies have been performed to determine whether transection or preservation of the C2 nerve root affects patient-derived sensory outcomes.PURPOSE:The purpose of this study is to specifically analyze patient-derived sensory outcomes over time in patients with intentional C2 nerve root transection during atlantoaxial segmental screw fixation compared with those without transection.STUDY DESIGN:This is a post-hoc comparative analysis of prospectively collected patient-derived outcome data.PATIENT SAMPLE:The sample consists of 24 consecutive patients who underwent intentional bilateral transection of the C2 nerve root during posterior atlantoaxial segmental screw fixation (transection group) and subsequent 41 consecutive patients without transection (preservation group).OUTCOME MEASURES:A visual analog scale (VAS) score was used for occipital neuralgia as the primary outcome measure and VAS score for neck pain, neck disability index score and Japanese Orthopedic Association score for cervical myelopathy and recovery rate, with bone union rate as the secondary outcome measure.METHODS:Patient-derived outcomes including change in VAS score for occipital neuralgia over time were statistically compared between the two groups. This study was not supported by any financial sources and there is no topic-specific conflict of interest related to the authors of this study.RESULTS:Seven (29%) of the 24 patients in the transection group experienced increased neuralgic pain at 1 month after surgery either because of newly developed occipital neuralgia or aggravation of preexisting occipital neuralgia. Four of the seven patients required almost daily medication even at the final follow-up (44 and 80 months). On the other hand, only four (10%) of 41 patients in the preservation group had increased neuralgic pain at 1 month after surgery, and at ≥1 year, no patients had increased neuralgic pain. The difference in the prevalence of increased neuralgic pain between the two groups was statistically significant at all time points (3, 6, 12, and 24 months postoperatively) except at 1 month postoperatively. The intensity of neuralgic pain, which preoperatively had not been significantly different between the two groups, was significantly higher in the transection group at the final follow-up.CONCLUSIONS:C2 nerve root transection is not a benign procedure and, in our experience, more than a quarter of the patients experience increased neuralgic pain following C2 nerve root transection. Because the prevalence and intensity of postoperative neuralgia was significantly higher with C2 nerve root transection than with its preservation, we recommend against routine C2 nerve root transection when performing atlantoaxial segmental screw fixation.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000004226/8SEQ:8PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000004226ADJUST_YN:NEMP_ID:A076317DEPT_CD:801CITE_RATE:3.29FILENAME:postoperative occipital neuralgia.pdfDEPT_NM:의학과EMAIL:[email protected]_YN:YCONFIRM:

Ceramic fracture following cervical disc arthroplasty

Although ceramic fractures have been reported following total hip arthroplasty1-6, with an incidence ranging from 0.004% to 1.4%1-3, no cases of ceramic fracture following cervical disc arthroplasty have been reported, to our knowledge. We present the case of a patient with cervical radiculopathy who underwent total disc replacement at C5-C6 and C6-C7, which was complicated by the development of recurrent symptoms approximately one month after the index procedure. At the time of the revision surgery, the ceramic insert at the C6-C7 level was found to be fractured on its convex cranial side. The implant used was a semiconstrained ceramicon- ceramic prosthesis (Discocerv Cervidisc Evolution; Scientx, Guyancourt, France). Since the introduction of this prosthesis in April 20067, more than 2000 prostheses have been implanted. The patient was informed that data concerning the case would be submitted for publication, and he gave his consent.Copyright(2011) THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED. The following article appeared in (citation of published article) and may be found at related URL.OAIID:oai:osos.snu.ac.kr:snu2011-01/102/0000004226/8SEQ:8PERF_CD:SNU2011-01EVAL_ITEM_CD:102USER_ID:0000004226ADJUST_YN:NEMP_ID:A076317DEPT_CD:801CITE_RATE:3.272FILENAME:E036T_JBJS-A-2011_Nguyen_Ceramic fracture following cervical disc arthroplasty.pdfDEPT_NM:의학과EMAIL:[email protected]_YN:NCONFIRM: