On the Complexity of Learning from Drifting Distributions

Information and Computation1382170-193INFC

Red-Black Prefetching: An Approximation Algorithm for Parallel Disk Scheduling

. We address the problem of I/O scheduling of read-once reference strings in a multiple-disk parallel I/O system. We present a novel online algorithm, Red-Black Prefetching (RBP), for parallel I/O scheduling. In order to perform accurate prefetching RBP uses L-block lookahead. The performance of RBP is analyzed in the standard parallel disk model with D independent disks and a shared I/O buffer of size M . We show that the number of parallel I/Os performed by RBP is within a factot \Theta(maxf p MD=L;D 1=3 g) of the number of I/Os done by the optimal offline algorithm. This ratio is within a canstant factor of the best possible when L is L = O(MD 1=3 ). 1 Introduction Continuing advances in processor architecture and technology have resulted in the I/O subsystem becoming the bottleneck in many applications. The problem is exacerbated by the advent of multiprocessing systems that can harness the power of hundreds of processors in speeding up computation. Improvements in I/O tech..

Scheduling Multiple Flows on Parallel Disk Systems

Abstract. We examine the problem of scheduling concurrent independent flows on multiple-disk I/O storage systems. Two models are considered: in the shared buffer model the memory buffer is shared among all the disks, while in the partitioned buffer model each flow has a private buffer. For the parallel disk model with d> 1 disks it is shown that the problem of minimizing the schedule length of n> 2 concurrent flows is NP-complete for both buffer models. A randomized scheduling algorithm for the partitioned buffer model is analyzed and probabilistic bounds on the schedule length are presented. Finally a heuristic based on static buffer allocation for the shared buffer model is discussed.

Correla??o dos n?veis de anticorpos ANTI-HLA de classe I e II doador espec?ficos detectados por ensaio de fase s?lida com os resultados das provas cruzadas no pr?-transplante renal

Submitted by Setor de Tratamento da Informa??o - BC/PUCRS ([email protected]) on 2015-05-28T12:30:06Z No. of bitstreams: 1 469532 - Texto Completo.pdf: 772339 bytes, checksum: b1ca6d60639abd0248f0ea693f8f7d1f (MD5)Made available in DSpace on 2015-05-28T12:30:06Z (GMT). No. of bitstreams: 1 469532 - Texto Completo.pdf: 772339 bytes, checksum: b1ca6d60639abd0248f0ea693f8f7d1f (MD5) Previous issue date: 2015-03-04Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPESIntroduction: There has been a continuous search for safe tests that can predict antibody-mediated rejection in organ transplants, and the positive complement dependent cytotoxic crossmatch, developed in the 1960?s, was until recently considered the gold standard and the main test for prediction of rejection. The new methods for assessing humoral immunity, notably flow cytometric crossmatching and the Luminex? technology significantly increased the sensitivity of these assessments, but also the complexity in the interpretation of these results, as well as in the correlation of different methodologies. Despite the sensitivity of these methods, not any donor-specific antibody detected by solid phase assay results in positive or negative crossmatch. Information obtained with the specificities (such as fluorescence intensity) of anti-HLA antibodies may define the immunological risk for the patient, assisting in the selection of the ideal donor, as well as in the immunosuppressive regimen, for prophylactic and therapeutic uses. Objectives: The present study aimed to establish a cut-off point at the fluorescence intensity of antibodies detected by the panel Single Antigen Beads of class I and II that correlates to positive flow cytometric crossmatching (FCXM). It also aimed to assess whether there are differences between the use of DSAs with higher MFI alone and the sum of all the DSAs of a given patient. Methodology: A cross-sectional study of two databases of results of panels (Luminex?) and flow cytometric crossmatching of patients on a waiting list for kidney transplantation registered at the Laborat?rio de Imunologia de Transplantes da Santa Casa de Miseric?rdia, in Porto Alegre. Database 1 was composed of 1,316 crossmatches against deceased donors and panels of anti-HLA antibodies for loci A, B and DRB1 performed in 2010. Database 2 was composed of 2,288 crossmatches against deceased donors and panels of anti-HLA antibodies for loci C and DQB1 performed between July 2013 and July 2014. As an inclusion criterion for both databases, only samples with results available in the Panel on the same date of the serum tested in flow cytometry crossmatches were used resulting in 834 samples in database 1. Besides, for database 2 only samples with donor-specific antibody (DSA) for loci C and or DQB1, resulting in 348 crossmatches. Results and Conclusions: we demonstrated that 97.6% of the patients with DSAs anti-HLA- ABDRB1 with MFI ? 5000 resulted in positive FCXM. These were the optimal MFI cut-off values for donor selection when we assessed sensitivity and specificity for correlation with positive flow cytometric crossmatching. For DSAs HLA-DQB1, fluorescence intensities above 15,000 MFI offer high specificity (97.8%). Anti-HLA-C sensitization is less frequent (n=40). Only 5 patients showed MFI?5000. Of these, the crossmatch was positive in only one patient (20%). Virtual crossmatch is a resource that can assist in making pre-kidney transplantation decisions.Introdu??o: A busca por testes seguros que possam prever a rejei??o mediada por anticorpo em transplantes de ?rg?os tem sido cont?nua e a prova cruzada por citotoxicidade dependente de complemento, desenvolvida na d?cada de 60, at? pouco tempo era considerada padr?o ouro e principal teste preditor de rejei??o. Os novos m?todos de aferi??o da imunidade humoral, notadamente a prova cruzada por citometria de fluxo e a tecnologia Luminex?, aumentaram significativamente a sensibilidade destas avalia??es, mas tamb?m a complexidade na interpreta??o destes resultados, assim como na correla??o das diferentes metodologias Embora bastante sens?vel, nem todo anticorpo doador espec?fico detectado pelo teste de fase s?lida resulta em uma prova cruzada positiva ou com rejei??o. As informa??es obtidas com as especificidades (assim como a intensidade de fluoresc?ncia) dos anticorpos anti-HLA podem definir o risco imunol?gico do paciente, auxiliando a escolha do doador ideal, bem como do esquema imunossupressor, tanto profil?tico quanto terap?utico. Objetivos: O objetivo deste trabalho foi estabelecer um ponto de corte no n?vel de fluoresc?ncia de anticorpos detectados pelo painel Single Antigen Beads de classe I e II que se correlacione com a prova cruzada positiva por citometria de fluxo (XMCF). Tamb?m objetivou-se avaliar se existem diferen?as entre o emprego de apenas DSAs com maior MFI e a soma de todos os DSAs de um determinado paciente. Metodologia: Foi realizado estudo transversal de dois bancos de dados de resultados de Paineis (Luminex?) e prova cruzada por citometria de fluxo de pacientes em lista de espera para transplante renal cadastrados no Laborat?rio de Imunologia de Transplantes da Santa Casa de Miseric?rdia de Porto Alegre. O banco n?mero 1 era composto de 1316 provas cruzadas contra doadores falecidos e pain?is de anticorpos anti-HLA dos loci A, B e DRB1, realizados no ano de 2010. O banco n?mero dois era composto de 2288 provas cruzadas contra doadores falecidos e pain?is de anticorpos anti-HLA dos loci C e DQB1 realizadas entre julho de 2013 e julho de 2014. Como crit?rio de inclus?o para ambos os bancos de dados foram utilizadas somente amostras que possu?am resultados de Painel na mesma data do soro testado nas provas cruzadas por citometria de fluxo, resultando em 834 amostras no banco de n?mero 1. Al?m disso, para o banco de dados n?mero 2 foram utilizados apenas amostras que possu?am anticorpo espec?fico contra o doador (DSA) dos loci C e ou DQB1, resultando em 348 provas cruzadas. Resultados e Conclus?es: demonstramos que 97,6% dos pacientes com DSAs anti-HLA- ABDRB1 com MFI?5000 resultaram em XMCF positiva. Os n?veis de MFI nesta faixa corresponderam aos melhores pontos de corte de escolha quando avaliamos a sensibilidade e especificidade para a correla??o com a prova cruzada positiva por citometria de fluxo. Para os DSAs HLA-DQB1, n?veis de fluoresc?ncia acima de 15.000 MFI ofereceram elevada especificidade (97,8%). A sensibiliza??o anti-HLA-C ? menos frequente (n=40). Apenas 5 pacientes apresentaram MFI?5000. Destes, apenas em um (20%) a prova cruzada foi positiva. A prova cruzada virtual ? um recurso que pode auxiliar na tomada de decis?es pr?-transplante renal

Algorithms for Scalable Storage Servers

We survey a set of algorithmic techniques that make it possible to build a high performance storage server from a network of cheap components. Such a storage server oers a very simple programming model. To the clients it looks like a single very large disk that can handle many requests in parallel with minimal interference between the requests