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ON BLOCK mATRICES ASSOCIATED WITH DISCRETE TRIGONOmETRIC TRANSFORmS AND THEIR USE IN THE THEORY OF WAVE PROPAGATION

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Journal of Computational mathematics 2010年第6期28卷 864-878页

作者： nikolaos L.Tsitsas School of Applied mathematical and Physical Sciences National Technical University of Athens

Block matrices associated with discrete Trigonometric transforms （DTT＇s） arise in the mathematical modelling of several applications of wave propagation theory including discretizations of scatterers and radiators with the method of moments, the Boundary Element method, and the method of Auxiliary Sources. The DTT＇s are represented by the Fourier, Hartley, Cosine, and Sine matrices, which are unitary and offer simultaneous diagonalizations of specific matrix algebras. The main tool for the investigation of the aforementioned wave applications is the efficient inversion of such types of block matrices. To this direction, in this paper we develop an efficient algorithm for the inversion of matrices with U-diagonalizable blocks （U a fixed unitary matrix） by utilizing the U- diagonalization of each block and subsequently a similarity transformation procedure. We determine the developed method＇s computational complexity and point out its high efficiency compared to standard inversion techniques. An implementation of the algorithm in matlab is given. Several numerical results are presented demonstrating the CPU-time efficiency and accuracy for ill-conditioned matrices of the method. The investigated matrices stem from real-world wave propagation applications.

关键词： Discrete Trigonometric transforms Block matrices Efficient inversion algorithms Wave radiation and scattering Numerical methods in wave propagation theory.

A LOW-FREQUENCY ELECTROmAGNETIC NEAR-FIELD INVERSE PROBLEm FOR A SPHERICAL SCATTERER

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Journal of Computational mathematics 2013年第5期31卷 439-448页

作者： nikolaos L. Tsitsas Department of Informatics Aristotle University of Thessaloniki Thessaloniki Greece

The interior low-frequency electromagnetic dipole excitation of a dielectric sphere is uti- lized as a simplified but realistic model in various biomedical applications. motivated by these considerations, in this paper, we investigate analytically a near-field inverse scatter- ing problem for the electromagnetic interior dipole excitation of a dielectric sphere. First, we obtain, under the low-frequency assumption, a closed-form approximation of the series of the secondary electric field at the dipole＇s location. Then, we utilize this derived approx- imation in the development of a simple inverse medium scattering algorithm determining the sphere＇s dielectric permittivity. Finally, we present numerical results for a human head model, which demonstrate the accurate determination of the complex permittivity by the developed algorithm.

关键词： Near-field inverse problems Low-frequency region Dipoles Hypergeometricfunctions.

On the Termination of Flips for Log Canonical Generalized Pairs

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Acta mathematica Sinica,English Series 2023年第6期39卷 967-994页

作者： Guo Du CHEN nikolaos TSAKANIKAS Institute for Theoretical Sciences Westlake Institute for Advanced StudyWestlake UniversityHangzhou 310024P.R.China Fachrichtung mathematik CampusGebäude E24Universität des Saarlandes66123 SaarbrückenGermany

We prove the termination of flips for pseudo-effective NQC log canonical generalized pairs of dimension *** main ingredients,we verify the termination of flips for 3-dimensional NQC log canonical generalized pairs,and show that the termination of flips for pseudo-effective NQC log canonical generalized pairs which admit NQC weak Zariski decompositions follows from the termination of flips in lower dimensions.

关键词： minimal model Program generalized pairs termination of fips special termination weak Zariski decompositions

A new approach for scheduling of multipurpose batch processes with unlimited intermediate storage policy

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Frontiers of Chemical Science and Engineering 2019年第4期13卷 784-802页

作者： nikolaos Rakovitis Nan Zhang Jie Li Liping Zhang Centre for Process Integration School of Chemical Engineering and Analytical ScienceThe University of ManchesterManchesterM139PLUK Department of Industrial Engineering School of Machinery and AutomationWuhan University of Science and TechnologyWuhan 430081China

The increasing demand of goods,the high competitiveness in the global marketplace as well as the need to minimize the ecological footprint lead multipurpose batch process industries to seek ways to maximize their productivity with a simultaneous reduction of raw materials and utility consumption and efficient use of processing *** scheduling of their processes can lead facilities towards this *** a great number of mathematical models have been developed for such scheduling,they may still lead to large model sizes and computational *** this work,we develop two novel mathematical models using the unit-specific eventbased modelling approach in which consumption and production tasks related to the same states are allowed to take place at the same event *** computational results demonstrate that both proposed mathematical models reduce the number of event points *** proposed unit-specific event-based model is the most efficient since it both requires a smaller number of event points and significantly less computational time in most cases especially for those examples which are computationally expensive from existing models.

关键词： scheduling multipurpose batch processes simultaneous transfer mixed-integer linear programming

Resection of isolated liver oligometastatic disease in pancreatic ductal adenocarcinoma:Is there a survival benefit?A systematic review

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World Journal of Gastrointestinal Surgery 2023年第7期15卷 1512-1521页

作者： James m Halle-Smith Sarah Powell-Brett Keith Roberts nikolaos A Chatzizacharias Department of HPB and Liver Transplant Queen Elizabeth HospitalUniversity of BirminghamBirmingham B152GWUnited Kingdom

BACKGROUND Presence of liver metastatic disease in pancreatic ductal adenocarcinoma(PDAC),either synchronous or metachronous after pancreatic resection,is a terminal diagnosis that warrants management with palliative intent as per all international practice ***,there is an increasing interest on any potential value of surgical treatment of isolated oligometastatic disease in selected *** To present the published evidence on surgical management of PDAC liver metastases,synchronous and metachronous,and compare the outcomes of these treatments to the current standard of *** A systematic review was performed in line with the Preferred Reporting Items for Systematic Review and meta-Analyses guidelines to compare the outcomes of both synchronous and metachronous liver metastases resection to standard *** 356 studies were identified,31 studies underwent full-text review and of these 10 were suitable for *** synchronous resection of liver metastases was compared to standard care,most studies did not demonstrate a survival benefit with the exception of one study that utilised neoadjuvant ***,resection of metachronous disease appeared to confer a survival advantage when compared to treatment with chemotherapy *** A survival benefit may exist in resection of selected cases of metachronous liver oligometastatic PDAC disease,after disease biology has been tested with time and systemic *** survival benefit is less clear in synchronous cases;however an approach with neoadjuvant treatment and consideration of resection in some selected cases may confer some *** studies should focus on pathways for selection of cases that may benefit from an aggressive approach.

关键词： Pancreas cancer Liver metastases Surgical resection Systematic review

Recurring heavy rainfall resulting in degraded-upgraded phases in soil microbial networks that are reflected insoil functioning

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Soil Ecology Letters 2023年第3期5卷 75-88页

作者： George P.Stamou nikolaos monokrousos Anastasia Papapostolou Effimia m.Papatheodorou Department of Ecology School of BiologyAristotle UniversityThessaloniki 54124Greece University Center of International Programmes of Studies International Hellenic UniversityThessaloniki 57001Greece

Biological soil crusts(BSCs)are an important multi-trophic component of arid ecosystems in the mediterranean *** a mesocosm experiment,the authors investigated how the network of interactions among the members of the soil microbial communities in four types of soil sample responded when soils were exposed to two simulated extreme rain *** four types of soil samples were:covered by Cladonia rangiformis and previously hydrated(+BSC+H),covered by *** and dried(+BSC-H),uncovered and hydrated(-BSC+H),uncovered and dried(-BSC-H).Network analysis was based on the co-occurrence patterns of microbes;microbes were assessed by the phospholipid fatty acids *** authors further explored the relations between networks’metrics and soil functions denoted by enzymatic activity and soil chemical *** networks exhibited Small world properties,moderate values of clustering coefficient and eigen centrality,indicating the lack of hub *** networks in-BSC-H soils appeared coherent during the pre-rain phases and they became modular after rains,while those in+BSC-H soils kept their connectivity till the second rain but this then *** network metrics that were indicative of cohesive networks tended to be related to enzyme activity while those that characterized the loose networks were related to Ca,K,mg,NH_(4)^(+) and organic *** all mesocosms except for+BSC-H,networks’fragmentation after the second heavy rain was milder than after the first one,supporting the idea of community *** response of microbial networks to heavy rains was characterized by the tendency to exhibit degradation-reconstruction *** network collapse in the crusted only mesocosms showed that the communities beneath crusts in arid areas were extremely vulnerable to recurring heavy rain events.

关键词： PLFAs Cladonia rangiformis biocrust soil microbial community network metrics

Cannabis use history is associated with increased prevalence of ascites among patients with nonalcoholic fatty liver disease:A nationwide analysis

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World Journal of Hepatology 2020年第11期12卷 993-1003页

作者： Catherine J Choi Stanley H Weiss Umair m Nasir nikolaos T Pyrsopoulos Department of medicine Rutgers New Jersey Medical SchoolNewarkNJ 07101United States Department of medicine Biostatistics and EpidemiologyRutgers New Jersey Medical SchoolNewarkNJ 07103United States Division of Gastroenterology and Hepatology Department of MedicineRutgers-New Jersey Medical SchoolNewarkNJ 07103United States

BACKGROUND Recent studies have revealed the endocannabinoid system as a potential therapeutic target in the management of nonalcoholic fatty liver disease(NAFLD).Cannabis use is associated with reduced risk for NAFLD,we hypothesized that cannabis use would be associated with less liver-related clinical complications in patients with *** To assess the effects of cannabis use on liver-related clinical outcomes in hospitalized patients with *** We performed a retrospective matched cohort study based on querying the 2014 National Inpatient Sample(NIS)for hospitalizations of adults with a diagnosis of *** NIS database is publicly available and the largest all-payer inpatient database in the United *** patients with cannabis use were selected as cases and those without cannabis were selected as ***-control matching at a ratio of one case to two controls was performed based on sex,age,race,and *** liver-related outcomes such as portal hypertension,ascites,varices and variceal bleeding,and cirrhosis were compared between the *** A total of 49911 weighed hospitalizations with a diagnosis of NAFLD were *** these,3820 cases were selected as the cannabis group,and 7625 noncannabis cases were matched as *** with cannabis use had a higher prevalence of ascites(4.5%vs 3.6%),with and without cannabis use,P=*** prevalence of portal hypertension(2.1%vs 2.2%),varices and variceal bleeding(1.3%vs 1.7%),and cirrhosis(3.7%vs 3.6%)was not different between the groups,with and without cannabis use,all P>***,race/ethnicity other than White,Black,Asian,Pacific Islander or Native American,and higher comorbidity score were independent risk factors for ascites in the cannabis *** non-cannabis users,obesity and hyperlipidemia were independent protective factors against ascites while older age,Native American and higher comorbidity index were independent risk factors for ***

关键词： Nonalcoholic fatty liver disease Fatty liver Cannabis marijuana use Liver diseases Hospitalization

A benchtop brain injury model using resected donor tissue from patients with Chiari malformation

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Neural Regeneration Research 2023年第5期18卷 1057-1061页

作者： Jacqueline A.Tickle Jon Sen Christopher Adams David N.Furness Rupert Price Viswapathi Kandula nikolaos Tzerakis Divya m.Chari Aston Pharmacy School College of Health and Life SciencesAston UniversityBirminghamUK School of medicine Faculty of Medicine and Health SciencesKeele UniversityStaffordshireUK School of Life Sciences Keele UniversityStaffordshireUK Department of Neurosurgery Royal Stoke University HospitalStoke-on-TrentUK

The use of live animal models for testing new therapies for brain and spinal cord repair is a controversial area. Live animal models have associated ethical issues and scientific concerns regarding the predictability of human responses. Alternative models that replicate the 3 D architecture of the central nervous system have prompted the development of organotypic neural injury models. However, the lack of reliable means to access normal human neural tissue has driven reliance on pathological or post-mortem tissue which limits their biological utility. We have established a protocol to use donor cerebellar tonsillar tissue surgically resected from patients with Chiari malformation(cerebellar herniation towards the foramen magnum, with ectopic rather than diseased tissue) to develop an in vitro organotypic model of traumatic brain injury. Viable tissue was maintained for approximately 2 weeks with all the major neural cell types detected. Traumatic injuries could be introduced into the slices with some cardinal features of post-injury pathology evident. Biomaterial placement was also feasible within the in vitro lesions. Accordingly, this ‘proof-of-concept’ study demonstrates that the model offers potential as an alternative to the use of animal tissue for preclinical testing in neural tissue engineering. To our knowledge, this is the first demonstration that donor tissue from patients with Chiari malformation can be used to develop a benchtop model of traumatic brain injury. However, significant challenges in relation to the clinical availability of tissue were encountered, and we discuss logistical issues that must be considered for model scale-up.

关键词： biomaterial Chiari malformation cerebellar slice human tissue injury model neuroregeneration organotypic traumatic brain injury

Colonic and anal metastases from pancreato-biliary malignancies

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World Journal of Gastroenterology 2014年第13期20卷 3693-3697页

作者： Farshid Ejtehadi nikolaos A Chatzizacharias Rebecca J Brais Nigel R Hall Edmund m Godfrey Emmanuel Huguet Raaj K Praseedom Asif Jah Department of HPB and Transplant Surgery Addenbrooke’s HospitalCambridge University Hospitals NHS Foundation TrustCambridgeshire CB2 0QQUnited Kingdom Department of Histopathology Addenbrooke’s HospitalCambridge University Hospitals NHS Foundation TrustCambridgeshire CB2 0QQUnited Kingdom Cambridge Colorectal Unit Addenbrooke’s HospitalCambridge University Hospitals NHS Foundation TrustCambridgeshireCB2 0QQUnited Kingdom Department of Radiology Addenbrooke’s HospitalCambridge University Hospitals NHS Foundation TrustCambridgeshire CB2 0QQUnited Kingdom

Pancreato-biliary malignancies often present with locally advanced or metastatic *** is the mainstay of treatment although less than 20%of tumours are suitable for resection at *** sites for metastases are liver,lungs,lymph nodes and peritoneal *** disease carries poor prognosis,with median survival of less than 3 *** report two cases where metastases from pancreato-biliary cancers were identified in the colon and anal *** both cases specific immunohistochemical staining was utilised in the *** the first case,the pre-senting complaint was obstructive jaundice due to an ampullary tumour for which a pancreato-duodenectomy was carried ***,the patient re-presented 4wk later with an atypical anal fissure which was found to be metastatic deposit from the primary ampullary *** the second case,the patient presented with obstructive jaundice due to a biliary *** imaging revealed sigmoid thickening,which was confirmed to be a metastatic *** colonic and anorectal metastases from pancreatobiliary cancers are rare and can masquerade as primary colorectal *** key to the diagnosis is the specific immunohistochemical profile of the intestinal lesion biopsies.

关键词： Pancreatobiliary cancer Rare metastatic sites Colonic metastasis Anal metastasis Immunohistochemistry