Using an azobenzene cross-linker to either increase or decrease peptide helix content upon trans-to-cis photoisomerization

Reversible photocontrol of peptide and protein conformation could prove to be a powerful tool for probing function in diverse biological systems. Here, we report reversible photoswitching of the helix content in short peptides containing an azobenzene cross-linker between cysteine residues at positions i, i + 4, or i, i + 11 in the sequence. Trans-to-cis photoisomerization significantly increases the helix content in the i, i + 4 case and significantly decreases the helix content in the i, i + 11 case. These cross-linker designs significantly expand the possibilities for photocontrol of peptide and protein structure.     

Overview of the effects of solar-terrestrial phenomena on man and his environment

Summary The effect of solar-terrestrial phenomena on our environment is a rapidly developing science. An overview of this subject is presented including known technological effects, possible effects on ozone depletion, and the much more elusive possibility that solar emissions may be linked to human health. Paper presented at the Special Session on the effects of solar-terrestrial phenomena on man and his environment of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

A multidimensional continued fraction based on a high-order recurrence relation

The paper describes and studies an iterative algorithm for finding small values of a set of linear forms over vectors of integers. The algorithm uses a linear recurrence relation to generate a vector sequence, the basic idea being to choose the integral coefficients in the recurrence relation in such a way that the linear forms take small values, subject to the requirement that the integers should not become too large. The problem of choosing good coefficients for the recurrence relation is thus related to the problem of finding a good approximation of a given vector by a vector in a certain one-parameter family of lattices; the novel feature of our approach is that practical formulae for the coefficients are obtained by considering the limit as the parameter tends to zero. The paper discusses two rounding procedures to solve the underlying inhomogeneous Diophantine approximation problem: the first, which we call ``naive rounding' leads to a multidimensional continued fraction algorithm with suboptimal asymptotic convergence properties; in particular, when it is applied to the familiar problem of simultaneous rational approximation, the algorithm reduces to the classical Jacobi-Perron algorithm. The second rounding procedure is Babai's nearest-plane procedure. We compare the two rounding procedures numerically; our experiments suggest that the multidimensional continued fraction corresponding to nearest-plane rounding converges at an optimal asymptotic rate.

     

Evidence for the quantum birth of our universe

We present evidence for a nonsingular origin of the Universe with intial conditions determined by quantum physics and relativistic gravity. In particular, we establish that the present temperature of the microwave background and the present density of the Universe agree well with our predictions from these intial conditions, after evolution to the present age using the Einstein-Friedmann equation. Remarkably, the quantum origin for the Universe naturally allows its evolution at exactly the critical density. We also discuss the consequences of these results to some fundamental aspects of quantum physics in the early Universe.     

On cosmic-ray cut-off terminology

Summary The study of cosmic-ray access to locations within the geomagnetic field has evolved over the past fifty years. Cosmic-ray cut-off terminology, originally developed to describe particle access and cut-off rigidities, has not evolved with the scientific advances in the field, and misunderstandings and misapplications of historical work have occurred. This paper is an attempt to remedy this situation by clarifying the areas in which changes have occurred and by providing a cross reference between the historical terms and those terms now in use for innovative cosmic-ray studies which are underway in several laboratories.     

Use of electrodeposition for sample preparation and rejection rate prediction for assay of electroformed ultra high purity copper for 232Th and 238U prior to inductively coupled plasma mass spectrometry (ICP/MS)

The search for neutrinoless double beta decay in ⁷⁶Ge has driven the need for ultra-low background Ge detectors shielded by electroformed copper of ultra-high radiopurity (<0.1 μBq/kg). Although electrodeposition processes are almost sophisticated enough to produce copper of this purity, to date there are no methods sensitive enough to assay it. Inductively coupled plasma mass spectrometry (ICP/MS) can detect thorium and uranium at femtogram levels, however, this assay is hindered by high copper concentrations in the sample. Electrodeposition of copper samples removes copper from the solution while selectively concentrating thorium and uranium contaminants to be assayed by ICP/MS. Spiking ²³²Th and ²³⁸U into the plating bath simulates low purity copper and allows for the calculation of the electrochemical rejection rate of thorium and uranium in the electroplating system. This rejection value will help to model plating bath chemistry.     

The effect of altitude differences and secular changes on the utilization of cosmic-ray variational coefficients

Summary The extended sets of variational coefficients have been examined to ascertain the effects of altitude and also for possible effects due to secular changes in the Earth magnetic field. A comparison of the variational coefficients calculated for two closely positioned cosmic-ray stations (Bagnères de Bigorre and Pic du Midi) indicates that the altitude effects are small. An examination of the variational coefficients calculated for western hemispheric locations, where the geomagnetic field has its most rapid secular change, indicates a maximum phase difference of one-half hour in the first harmonic of the daily variation. Significant changes of the phase of transient anisotropies can be computed only for unreallistic cases of extremely narrow ?square wave? modulations. The results of this analysis indicate that the secular variation in the vertical cut-off rigidity (and associated changes in the asymptotic-direction calculations) are such that variational coefficients calculated by using either a 1955 or a 1975 model of the geomagnetic field are adequate for most cosmic-ray analyses.

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Riassunto Si sono esaminati i gruppi estesi di coefficienti di variazione per accertare gli effetti dell’altitudine e anche per i possibili effetti dovuti ai cambiamenti secolari del campo magnetico terrestre. Un confronto dei coefficienti di variazione calcolati per due stazioni di raggi cosmici poste molto vicine (Bagnères de Bigorre e Pic du Midi) indica che gli effetti dell’altitudine sono piccoli. Un esame dei coefficienti di variazione calcolati per stazioni dell’emisfero occidentale dove il campo magnetico ha il suo più rapido cambiamento secolare, indica un massimo di differenza di fase di mezz’ora nella prima armonica della variazione diurno. Cambiamenti significativi della fase di anisotropie transitorie possono essere calcolati per casi non realistici di modulazioni estremamente piccole di ?onda quadrata?. I risultati di questa analisi indicano che la variazione secolare nella rigidità verticale di taglio (e i cambiamenti associati nei calcoli delle direzioni asimptotiche) sono tali che i coefficienti di variazione calcolati usando sia un modello di campo magnetico del 1955 che uno del 1975 sono adatti per la maggior parte delle analisi dei raggi cosmici.

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Резюме Исследуется система вариационных коэффициентов с целью определения эфектов высоты, а также возможных эффектов, обусловленных секулярными изменениями магнитного поля Земли. Сравнение вариационных коэффициентов, вычисленных для двух близко расположенных космических станций, указывает на то, что эффекты высоты являются малыми. Исследование вариационных коэффициентов, вычисленных для точек в западном полушарии, где геомагнитное поле имеет наиболее быстрое секулярное изменение, указывает на максимальную разность фаз в полчаса в первой гармонике для дневной вариации. Существенные изменения фазы для переходных анизотропий может быть вычислено только для нереалистических случаев чрезвычайно узких модуляций. Результаты этого анализа указывают, что секулярная вариация (и связанные изменения при вычислениях асимптотических направлений) являются такими, что вариационные коэффициенты, вычисленные с использованием модели 1955 или 1975 для геомагнитного поля, являются адекватными для большинства проведенных анализов космических дучей.

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