Gauge Invariant Action for the Open Bosonic String: Tachyon Action

A gauge invariant action for the open bosonic string has been proposed in an earlier paper. We work out the consequences of this proposal for the lowest mode, viz. the tachyon. The action can be calculated for generic momenta, perturbatively, order by order in the tachyon field. For on shell tachyons we explicitly calculate the cubic action and show that it reproduces the correct equations of motion and coincides wih the $\beta$ function to the required order. The calculation is done in terms of bare fields with a finite cutoff, which is the original prescription. We also show that it is possible in some momentum regions to renormalize the theory and eliminate the cutoff dependence so that the continuum limit can be taken. After renormalization, the parameter $R\over a$ is replaced by $R\over L$ where $R$ is an IR cutoff, $a$ is the UV cutoff and $L$ is some renormalization scale. There is also some arbitrariness in the overall normalization due to the choice of regularization scheme - this does not affect on-shell quantities. We also rederive within this scheme, the action in the region of zero momentum, which gives the exact (tree level) tachyon potential. The tachyon potential is consistent with Sen's conjecture that the height of the potential is the same as the tension of the brane.Comment: 31 pages, Late

ATM and Artemis promote homologous recombination of radiation-induced DNA double-strand breaks in G2

Homologous recombination (HR) and non‐homologous end joining (NHEJ) represent distinct pathways for repairing DNA double‐strand breaks (DSBs). Previous work implicated Artemis and ATM in an NHEJ‐dependent process, which repairs a defined subset of radiation‐induced DSBs in G1‐phase. Here, we show that in G2, as in G1, NHEJ represents the major DSB‐repair pathway whereas HR is only essential for repair of ∼15% of X‐ or γ‐ray‐induced DSBs. In addition to requiring the known HR proteins, Brca2, Rad51 and Rad54, repair of radiation‐induced DSBs by HR in G2 also involves Artemis and ATM suggesting that they promote NHEJ during G1 but HR during G2. The dependency for ATM for repair is relieved by depleting KAP‐1, providing evidence that HR in G2 repairs heterochromatin‐associated DSBs. Although not core HR proteins, ATM and Artemis are required for efficient formation of single‐stranded DNA and Rad51 foci at radiation‐induced DSBs in G2 with Artemis function requiring its endonuclease activity. We suggest that Artemis endonuclease removes lesions or secondary structures, which inhibit end resection and preclude the completion of HR or NHEJ

Simultaneous disruption of two DNA polymerases, Polη and Polζ, in Avian DT40 cells unmasks the role of Polη in cellular response to various DNA lesions

Replicative DNA polymerases are frequently stalled by DNA lesions. The resulting replication blockage is released by homologous recombination (HR) and translesion DNA synthesis (TLS). TLS employs specialized TLS polymerases to bypass DNA lesions. We provide striking in vivo evidence of the cooperation between DNA polymerase η, which is mutated in the variant form of the cancer predisposition disorder xeroderma pigmentosum (XP-V), and DNA polymerase ζ by generating POLη−/−/POLζ−/− cells from the chicken DT40 cell line. POLζ−/− cells are hypersensitive to a very wide range of DNA damaging agents, whereas XP-V cells exhibit moderate sensitivity to ultraviolet light (UV) only in the presence of caffeine treatment and exhibit no significant sensitivity to any other damaging agents. It is therefore widely believed that Polη plays a very specific role in cellular tolerance to UV-induced DNA damage. The evidence we present challenges this assumption. The phenotypic analysis of POLη−/−/POLζ−/− cells shows that, unexpectedly, the loss of Polη significantly rescued all mutant phenotypes of POLζ−/− cells and results in the restoration of the DNA damage tolerance by a backup pathway including HR. Taken together, Polη contributes to a much wide range of TLS events than had been predicted by the phenotype of XP-V cells

Chironomidae (Diptera, Insecta) do reservatório de Furnas (MG) e sua relação com a qualidade da água.

Resumo: Com a crescente expansão da criação de peixes em tanques rede advinda da prática da aquicultura, alterações na qualidade da água e em todo o ecossistema relacionado podem ocorrer. Sabe-se que a ocorrência de larvas de certas espécies da família Chironomidae (Diptera) associada a variáveis físicas e químicas da água pode ser adotada como indicador de impactos. Este trabalho teve como principal objetivo levantar a fauna de Chironomidae presente na área profundal do entorno de tanques rede no Reservatório de Furnas (MG) e determinar sua relação com a qualidade da água. O sedimento de fundo foi coletado com o auxílio de uma draga de Ekman-Birge, em tréplicas, em seis pontos com 16 m de profundidade em média, sendo um ponto localizado em área sem produção aquícola e os demais em pontos com produção. Após a coleta, as amostras foram triadas em laboratório utilizando-se microscópio estereoscópico e as larvas foram montadas em lâmina para identificação taxonômica em nível de gênero. Ao todo, 765 indivíduos foram identificados, sendo em sua maioria da subfamília Chironominae. Os indivíduos foram enquadrados em grupos tróficos funcionais, onde se encontrou uma maior abundância de indivíduos coletores catadores indicando alta concentração de matéria orgânica no sistema. Abstract: With the increasing expansion of fish farming in cages arising from the practice of aquaculture, changes in water quality and all related ecosystem may occur. It is known that the occurrence of larvae of certain species of the family Chironomidae (Diptera) associated with physical and chemical parameters can be adopted as an indicator of impacts. This study aimed to raise the Chironomidae fauna present in the deep area around cages in Furnas Reservoir (MG) and to determine its relationship with water quality. The bottom sediment was collected with the aid of an Ekman-Birge dredge in rejoinders in six points of 16 m deep on average, with a point located in an area without aquaculture and other on points with production. After collection, the samples were screened in the laboratory using a stereoscopic microscope and larvae were mounted on slides for taxonomic identification at genus level. In all, 765 individuals were identified, mostly subfamily Chironominae. Individuals were classified into functional feeding groups, where they found a greater abundance of individuals collectors gatherers indicating high concentration of organic matter in the system

On the Point-Splitting Method of the Commutator Anomaly of the Gauss Law Operators

We analyze the generalized point-splitting method and Jo's result for the commutator anomaly. We find that certain classes of general regularization kernels satisfying integral conditions provide a unique result, which, however differs from Faddeev's cohomological result.Comment: 16 pages, RevTex, 1 figure + 1 table, uses psbox.te

Conformal Symmetry and the Three Point Function for the Gravitational Axial Anomaly

This work presents a first study of a radiative calculation for the gravitational axial anomaly in the massless Abelian Higgs model. The two loop contribution to the anomalous correlation function of one axial current and two energy-momentum tensors, , is computed at an order that involves only internal matter fields. Conformal properties of massless field theories are used in order to perform the Feynman diagram calculations in the coordinate space representation. The two loop contribution is found not to vanish, due to the presence of two independent tensor structures in the anomalous correlator.Comment: 34 pages, 5 figures, RevTex, Minor changes, Final version for Phys. Rev.

N-String Vertices in String Field Theory

We give the general form of the vertex corresponding to the interaction of an arbitrary number of strings. The technique employed relies on the ``comma" representation of String Field Theory where string fields and interactions are represented as matrices and operations between them such as multiplication and trace. The general formulation presented here shows that the interaction vertex of N strings, for any arbitrary N, is given as a function of particular combinations of matrices corresponding to the change of representation between the full string and the half string degrees of freedom.Comment: 22 pages, A4-Latex (latex twice), FTUV IFI

Composição da comunidade macrobentônica no reservatório de Furnas (MG) em área de parque aquícola.

Resumo: O uso de métodos convencionais para análise da qualidade da água, como parâmetros físico-químicos, em áreas de reservatórios utilizadas para a agricultura, não é suficiente para detectar possíveis impactos gerados a longo prazo. Sendo assim, o uso de macroinvertebrados bentônicos como bioindicadores associado aos métodos convencionais se torna uma análise mais completa e abrangente. O trabalho apresenta dados do monitoramento da qualidade da água em uma área de parque aquícola do reservatório de Furnas, com enfoque no biomonitoramento da comunidade macrobentônica colonizadora do sedimento, em áreas com e sem produção de peixe. Foi observado que a comunidade biológica em estudo não apresentou alterações relacionadas com a produção aquícola, mas sim com a localização dentro do reservatório

The Sister-Chromatid Exchange Assay in Human Cells

The semiconservative nature of DNA replication allows the differential labeling of sister chromatids that isthe fundamental requirement to perform the sister-chromatid exchange (SCE) assay. SCE assay is apowerful technique to visually detect the physical exchange of DNA between sister chromatids. SCEscould result as a consequence of DNA damage repair by homologous recombination (HR) during DNAreplication. Here, we provide the detailed protocol to perform the SCE assay in cultured human cells. Cellsare exposed to the thymidine analog 5-bromo-20-deoxyuridine (BrdU) during two cell cycles, resulting inthe two sister chromatids having differential incorporation of the analog. After metaphase spreads prepara-tion and further processing, SCEs are nicely visualized under the microscope