Initial studies of array feeds for the 70-meter antenna at 32 GHz

The results of a study to determine the feasibility of using array feed techniques to improve the performance of the 70 m antenna at 32 GHz are presented. Changing from 8.4 to 32 GHz has the potential of increasing the gain by 11.6 dB, but recent measurements indicate that additional losses of from 3 to 7 dB occur at 32 GHz, depending on the elevation angle. Array feeds were proposed to recover some of the losses by compensating for surface distortions that contribute to these losses. Results for both surface distortion compensation and pointing error correction are discussed. These initial studies, however, had one significant restriction: The mechanical finite element model was used to characterize the surface distortions, not the measured distortions from three angle holography data, which would be more representative of the actual antenna. Further work is required to provide for a more accurate estimate of performance that utilizes holography data and, in particular, one that evaluates the performance in the focal plane region of the antenna

Conical quadreflex antenna analytical study

A method for evaluating the performance of a four-reflection or quadreflex antenna is reported. Geometrical optics was used initially to determine the ideal feed pattern required to produce uniform illumination on the aperture of the conical reflector and the reverse problem of quickly finding the aperture illumination given an arbitrary feed pattern. The knowledge of the aperture illumination makes it possible to compute the antenna efficiency, which is useful for comparing antenna performance during tradeoff studies. Scattering calculations, using physical optics techniques, were then used to more accurately determine the performance of a specific design

The pause-initiation limit restricts transcription activation in human cells.

Eukaryotic gene transcription is often controlled at the level of RNA polymerase II (Pol II) pausing in the promoter-proximal region. Pausing Pol II limits the frequency of transcription initiation ('pause-initiation limit'), predicting that the pause duration must be decreased for transcriptional activation. To test this prediction, we conduct a genome-wide kinetic analysis of the heat shock response in human cells. We show that the pause-initiation limit restricts transcriptional activation at most genes. Gene activation generally requires the activity of the P-TEFb kinase CDK9, which decreases the duration of Pol II pausing and thereby enables an increase in the productive initiation frequency. The transcription of enhancer elements is generally not pause limited and can be activated without CDK9 activity. Our results define the kinetics of Pol II transcriptional regulation in human cells at all gene classes during a natural transcription response

A Transactional Analysis of Interaction Free Measurements

The transactional interpretation of quantum mechanics is applied to the "interaction-free" measurement scenario of Elitzur and Vaidman and to the Quantum Zeno Effect version of the measurement scenario by Kwiat, et al. It is shown that the non-classical information provided by the measurement scheme is supplied by the probing of the intervening object by incomplete offer and confirmation waves that do not form complete transactions or lead to real interactions.Comment: Accepted for publication in Foundations of Physics Letter

Structural basis of TFIIH activation for nucleotide excision repair.

Nucleotide excision repair (NER) is the major DNA repair pathway that removes UV-induced and bulky DNA lesions. There is currently no structure of NER intermediates, which form around the large multisubunit transcription factor IIH (TFIIH). Here we report the cryo-EM structure of an NER intermediate containing TFIIH and the NER factor XPA. Compared to its transcription conformation, the TFIIH structure is rearranged such that its ATPase subunits XPB and XPD bind double- and single-stranded DNA, consistent with their translocase and helicase activities, respectively. XPA releases the inhibitory kinase module of TFIIH, displaces a 'plug' element from the DNA-binding pore in XPD, and together with the NER factor XPG stimulates XPD activity. Our results explain how TFIIH is switched from a transcription to a repair factor, and provide the basis for a mechanistic analysis of the NER pathway

Race, Culture & Abuse of Persons with Disabilities

This chapter will explore how race and culture influence the lives of persons with disabilities who are experiencing abuse. The discussion will be framed by an intersectional lens and will be informed by cultural humility and critical race theory. Practitioners need to remain open to the idea that they cannot and will not know all there is to know about any given culture, and they should be open to hearing about their clients’ understanding and experiences of culture. Rather than knowing certain pieces of “knowledge” about a cultural group, it is more important to understand what pieces of culture the clients embrace or reject. This chapter will conclude with a composite client case example of a female, middle-aged, Korean immigrant with Multiple Sclerosis, who is very active in her Christian church, and who is being abused by her husband. Discussion of this case will highlight the intersectional context of the client’s experience and how they may influence her decision to seek help (and from whom) as well as her experience of receiving help. The case discussion also highlights the practitioner’s values and behaviors that are consistent with cultural humility and critical race theory

Approximating open quantum system dynamics in a controlled and efficient way: A microscopic approach to decoherence

We demonstrate that the dynamics of an open quantum system can be calculated efficiently and with predefined error, provided a basis exists in which the system-environment interactions are local and hence obey the Lieb-Robinson bound. We show that this assumption can generally be made. Defining a dynamical renormalization group transformation, we obtain an effective Hamiltonian for the full system plus environment that comprises only those environmental degrees of freedom that are within the effective light cone of the system. The reduced system dynamics can therefore be simulated with a computational effort that scales at most polynomially in the interaction time and the size of the effective light cone. Our results hold for generic environments consisting of either discrete or continuous degrees of freedom