Low-temperature ion beam mixing of Pt and Si markers in Ge

The mixing of Pt and Si marker atoms in Ge during 750-keV Xe irradiation was measured at temperatures between 6 and 500 K. The low-temperature measurements show that the mixing parameter for Pt is nearly twice that for Si. This result is in strong contradiction to the collisional theory of ion beam mixing. A weak temperature dependence in the mixing is found for both markers

Roles of replication fork-interacting and Chk1-activating domains from claspin in a DNA replication checkpoint response

Claspin is essential for the ATR-dependent activation of Chk1 in Xenopus egg extracts containing incompletely replicated DNA. Claspin associates with replication forks upon origin unwinding. We show that Claspin contains a replication fork-interacting domain (RFID, residues 265–605) that associates with Cdc45, DNA polymerase ε, replication protein A, and two replication factor C complexes on chromatin. The RFID contains two basic patches (BP1 and BP2) at amino acids 265–331 and 470–600, respectively. Deletion of either BP1 or BP2 compromises optimal binding of Claspin to chromatin. Absence of BP1 has no effect on the ability of Claspin to mediate activation of Chk1. By contrast, removal of BP2 causes a large reduction in the Chk1-activating potency of Claspin. We also find that Claspin contains a small Chk1-activating domain (residues 776–905) that does not bind stably to chromatin, but it is fully effective at high concentrations for mediating activation of Chk1. These results indicate that stable retention of Claspin on chromatin is not necessary for activation of Chk1. Instead, our findings suggest that only transient interaction of Claspin with replication forks potentiates its Chk1-activating function. Another implication of this work is that stable binding of Claspin to chromatin may play a role in other functions besides the activation of Chk1

Freedom Of Speech And Censorship In The Internet

Internet censorship or internet content filtering is used to protect people from harmful materials, such as child pornography, as well as defamation and fraud, which are easily perpetrated on the internet. However, implementing censorship creates technical and social issues, such as over-blocking or false detection, decreased network performance, and freedom of speech. This paper describes internet content filtering approaches and technical difficulties to implementation. This paper also discusses censorship and freedom of speech with actual examples

Quantum linear amplifier enhanced by photon subtraction and addition

A deterministic quantum amplifier inevitably adds noise to an amplified signal due to the uncertainty principle in quantum physics. We here investigate how a quantum-noise-limited amplifier can be improved by additionally employing the photon subtraction, the photon addition, and a coherent superposition of the two, thereby making a probabilistic, heralded, quantum amplifier. We show that these operations can enhance the performance in amplifying a coherent state in terms of intensity gain, fidelity, and phase uncertainty. In particular, the photon subtraction turns out to be optimal for the fidelity and the phase concentration among these elementary operations, while the photon addition also provides a significant reduction in the phase uncertainty with the largest gain effect.Comment: published version, 7 pages, 9 figure

An ASCA Study of the W51 Complex

We present the analysis of ASCA archival data from the Galactic source W51. The ASCA spectra show that the soft (kT<= 2.5 keV) X-rays are of thermal origin and are compatible with W51C being a single, isothermal (kT~0.3 keV) supernova remnant at the far-side of the Sagittarius arm. The ASCA images reveal hard (kT>=2.5 keV) X-ray sources which were not seen in previous X-ray observations. Some of these sources are coincident with massive star-forming regions and the spectra are used to derive X-ray parameters. By comparing the X-ray absorbing column density with atomic hydrogen column density, we infer the location of star-forming regions relative to molecular clouds. There are unidentified hard X-ray sources superposed on the supernova remnant and we discuss the possibility of their association.Comment: 13 pages, 11 figures, to be published in Astronomical Journa

Online Task Groups and Social Work Education: Lessons Learned

This paper focuses the use of an online task group for social work students to solve problems and produce recommendations. An online site provides students the opportunity to edit documents produced by the group’s work. Online task groups provide an alternative to face-to-face task group meetings in social service agencies with a number of distant service delivery locations. Additionally, online task groups provide a cost effective way to accomplish the business of social service agencies by eliminating the time and cost of travel to attend meetings. This paper offers a stage model of online group development and a discussion of lessons learned from an online task group used in a graduate Clinical Supervision class