4,234 research outputs found
Investigation of Non-homogenous hidden Markov models and their Application to Spatially-distributed Precipitation Types
Precipitation is an important element in the hydrological cycle. To predict and simulate large-scale precipitation, Global Circulation Models (GCMs) are widely used. However, their grid scale is too big to apply to local hydrologic fields. In this study, non-homogenous hidden Markov models (NHMM) are explored as a means of generating the probability of precipitation occurrence in small scale given large-scaled weather patterns. Three different spatial models: (1) independent (2) auto-logistic (3) Chow-Liu tree, are also explored, along with methods and steps for parameter estimation. From this exploration, independent models with NHMM are recommended for very small precipitation networks, and the maximum likelihood method is found to be the most practical fitting method. If there are many points for downscaling, Chow-Liu tree models with the Expectation-Maximization (EM) algorithm are recommended. If more exact solutions are needed, auto-logistic models can be employed. If many points are considered in auto-logistic models, the (EM) algorithm should be used to estimate parameters separately and global optimization methods should be used for emission matrix. The major problem found with the NHMM model in this study is matching the rainfall amount for each year or month. This problem can be addressed by whether combining occurrence models with amount modes or by improving only occurrence models
Improving Predictions of Soil and Plant Evapotranspiration in Vadose Zone and Land Surface Models
This study focuses on the surface hydrology to contribute to its better parameterization through inter-comparison and direct improvement with two scopes: (1) soil evaporation process, and (2) the forest hydrological/physiological process based on Community Land Model (CLM). In soil evaporation study, the behaviors of the in-soil system and soil-atmosphere interface are explored and improved. The study of saturated front depths, under steady-state bare-soil evaporation, updates the previous method, which also provides a better understanding of the mechanism of the in-soil system. Through this investigation, the analytical and mass-conservative solution of the front depth is developed from Darcyās equation by applying two-direction flows in the soil system.
More importantly, applying soil-pore heterogeneity at the soil-atmosphere interface in the model has a significant influence on the evaporation rate. Through this study, a practical equation to use soil-pore heterogeneity is selected among known diffusion-based models (except empirical models) for the above the soil layer. Also, this study verifies the fully physical-based model about in and out soil system can mimic the behavior of bare-soil evaporation. The study of the canopy process identifies that CLM4.5&5 fail to capture the environmental complexity on tropical mountain rainforest in Costa Rica. The newer version (CLM5) shows some improvement. However, it still has discrepancies with observations. This study highlights the issue of the parameter for photosynthesis, but also the lack of in-canopy variability caused by overly simple model structure for sub-canopy layers and site-specific features (e.g., large/frequent precipitation, steep slope). Conversely, multi-layered CLM (CLM-ml) alleviates temperature-related variables and leaf wetness, and it is useful in self-diagnosing through the profiled observation. For this test, the CLM-ml is updated for an in-canopy turbulence transfer, canopy shape, and carbon dioxide (CO2) concentration profile. This study indicates updating sub-canopy structure (e.g., canopy shapes), and the parameter for the turbulent transfer model can have a significant influence on model performance. However, more extensive monitoring of sub-canopies is necessary to increase model reliability for this and other sites with complex terrain and vegetation roughness
Exploring Customersā Preferences for Online Games
Online content providers who use the Internet to distribute content experience an extremely competitive business environment. To survive in this environment, they have started charging a fee for the content that they provide. However, there have been very few success stories in commercializing online content. Although one of few success stories is the online game, it still has customersā psychological resistance against paying a high fee for playing games. To pay back their high R&D or development costs quickly, many online game producers have a tendency to assign high prices to their online games. Without examining customersā perceived prices for online games, many online game producers have tended to decide prices from their perspectives. Although many online game-related research works have focused on psychological and technical aspects, very few works have examined online gamersā preferences carefully. This study aims at exploring online gamersā preference by measuring their WTP (Willingness To Pay) for online games
Association of factor XIII Val34Leu polymorphism and coronary artery disease: A meta-analysis
Background: Factor XIII plays an important role in the stabilization of the linkage between fibrins and in the pathophysiology of coronary artery disease (CAD). The association between factor XIII Val34Leu polymorphism and CAD risk remains controversial.
Methods: We conducted a meta-analysis of 36 studies involving 26,940 cases and 34,694 controls. Subgroup analyses were performed with division of data into disease (myocardial infarction [MI], CAD without MI), age, and sex.
Results: Factor XIII Val34Leu polymorphism was significantly associated with ove all CAD risk (odds ratio [OR] = 1.09, 95% confidence interval [CI] = 1.03ā1.06, p = 0.004) and MI risk (OR = 1.15, 95% CI 1.07ā1.25, p = 0.0003), but not with CAD without MI risk (OR = 1.00, 95% CI 0.87ā1.15, p = 0.96). In the subgroup analysis by age and sex, there was no association between Val34Leu polymorphism and CAD.
Conclusions: This meta-analysis found that factor XIII Val34Leu polymorphism was associated with CAD risk, especially MI, but not with CAD without MI. In addition, age and sex did not affect the relationship between factor XIII Val34Leu polymorphism and CAD risk.
Intraoperative blood loss during different stages of scoliosis surgery: A prospective study
<p>Abstract</p> <p>Background</p> <p>There are a number of reasons for intraoperative blood loss during scoliosis surgery based on the type of approach, type of disease, osteopenia, and patient blood profile. However, no studies have investigated bleeding patterns according to the stage of the operation. The objective of this prospective study was to identify intraoperative bleeding patterns in different stages of scoliosis surgery.</p> <p>Methods</p> <p>We prospectively analyzed the estimated blood loss (EBL) and operation time over four stages of scoliosis surgery in 44 patients. The patients were divided into three groups: adolescent idiopathic (group 1), spastic neuromuscular (group 2) and paralytic neuromuscular (group 3). The per-level EBL and operation times of the groups were compared on a stage-by-stage basis. The bone marrow density (BMD) of each patient was also obtained, and the relationship between per-level EBL and BMD was compared using regression analysis.</p> <p>Results</p> <p>Per-level operation time was similar across all groups during surgical stage (p > 0.05). Per-level EBL was also similar during the dissection and bone-grafting states (p > 0.05). However, during the screw insertion stage, the per-level EBL was significantly higher in groups 2 and 3 compared to group 1 (p < 0.05). In the correction stage, per-level EBL was highest in group 3 (followed in order by groups 2 and 1) (p < 0.05). Preoperative BMD indicated that group 3 had the lowest bone quality, followed by groups 2 and 1 (in order), but the preoperative blood indices were similar in all groups. The differences in bleeding patterns in the screw insertion and correction stages were attributed to the poor bone quality of groups 2 and 3. Group 3 had the lowest bone quality, which caused loosening of the bone-screw interface during the correction stage and led to more bleeding. Patients with a T-score less than -2.5 showed a risk for high per-level EBL that was nine times higher than those with scores greater than -2.5 (p = 0.003).</p> <p>Conclusions</p> <p>We investigated the blood loss patterns during different stages of scoliosis surgery. Patients with poor BMD showed a risk of blood loss nine times higher than those with good BMD.</p
DS-ARP: A New Detection Scheme for ARP Spoofing Attacks Based on Routing Trace for Ubiquitous Environments
Despite the convenience, ubiquitous computing suffers from many threats and security risks. Security considerations in the ubiquitous network are required to create enriched and more secure ubiquitous environments. The address resolution protocol (ARP) is a protocol used to identify the IP address and the physical address of the associated network card. ARP is designed to work without problems in general environments. However, since it does not include security measures against malicious attacks, in its design, an attacker can impersonate another host using ARP spoofing or access important information. In this paper, we propose a new detection scheme for ARP spoofing attacks using a routing trace, which can be used to protect the internal network. Tracing routing can find the change of network movement path. The proposed scheme provides high constancy and compatibility because it does not alter the ARP protocol. In addition, it is simple and stable, as it does not use a complex algorithm or impose extra load on the computer system
Neuropathic Pain after Spinal Surgery
Neuropathic pain after spinal surgery, the so-called failed back surgery syndrome (FBSS), is a frequently observed troublesome disease entity. Although medications may be effective to some degree, many patients continue experiencing intolerable pain and functional disability. Only gabapentin has been proven effective in patients with FBSS. No relevant studies regarding manipulation or physiotherapy for FBSS have been published. Spinal cord stimulation (SCS) has been widely investigated as a treatment option for chronic neuropathic pain, including FBSS. SCS was generally accepted to improve chronic back and leg pain, physical function, and sleep quality. Although the cost effectiveness of SCS has been proved in many studies, its routine application is limited considering that it is invasive and is associated with safety issues. Percutaneous epidural adhesiolysis has also shown good clinical outcomes; however, its effects persisted for only a short period. Because none of the current methods provide absolute superiority in terms of clinical outcomes, a multidisciplinary approach is required to manage this complex disease. Further studies concerning the etiology, diagnosis, treatment, and cost effectiveness of FBSS are warranted to deepen our understanding of this condition
An Updated Overview of Low Back Pain Management in Primary Care
Currently, guidelines for lower back pain (LBP) treatment are needed. We reviewed the current guidelines and high-quality articles to confirm the LBP guidelines for the Korean Society of Spine Surgery. We searched available databases for high-quality articles in English on LBP published from 2000 to the present year. Literature searches using these guidelines included studies from MEDLINE, the Cochrane Database of Systematic Reviews, the Cochrane Central Register of Controlled Trials, and Embase. We analyzed a total of 132 randomized clinical trials, 116 systematic reviews, 9 meta-analyses, and 4 clinical guideline reviews. We adopted the SIGN checklist for the assessment of article quality. Data were subsequently abstracted by a reviewer and verified. Many treatment options exist for LBP, with a variety of recommendation grades. We assessed the recommendation grade for general behavior, pharmacological therapy, psychological therapy, and specific exercises. This information should be helpful to physicians in the treatment of LBP patients
The uncalibrated pulse contour cardiac output during off-pump coronary bypass surgery: performance in patients with a low cardiac output status and a reduced left ventricular function
BACKGROUND: We compared the continuous cardiac index measured by the FloTrac/Vigileoā¢ system (FCI) to that measured by a pulmonary artery catheter (CCI) with emphasis on the accuracy of the FCI in patients with a decreased left ventricular ejection fraction (LVEF) and a low cardiac output status during off-pump coronary bypass surgery (OPCAB). We also assessed the influence of several factors affecting the pulse contour, such as the mean arterial pressure (MAP), the systemic vascular resistance index (SVRI) and the use of norepinephrine.
METHODS: Fifty patients who were undergoing OPCAB (30 patients with a LVEF ā„ 40%, 20 patients with a LVEF < 40%) were enrolled. The FCI and CCI were measured and we performed a Bland-Altman analysis. Subgroup analyses were done according to the LVEF (< 40%), the CCI (ā¤ 2.4 L/min/m), the MAP (60-80 mmHg), the SVRI (1,600-2,600 dyne/s/cm(5)/m(2)) and the use of norepinephrine.
RESULTS: The FCI was reliable at all the time points of measurement with an overall bias and limit of agreement of -0.07 and 0.67 L/min/m(2), respectively, resulting in a percentage error of 26.9%. The percentage errors in the patients with a decreased LVEF and in a low cardiac output status were 28.2% and 22.3%, respectively. However, the percentage error in the 91 data pairs outside the normal range of the SVRI was 40.2%.
CONCLUSIONS: The cardiac output measured by the FloTrac/Vigileoā¢ system was reliable even in patients with a decreased LVEF and in a low cardiac output status during OPCAB. Acceptable agreement was also noted during the period of heart displacement and grafting of the obtuse marginalis branch.ope
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