Molecular dynamics calculations of the hard-sphere equation of state

The equation of state of the hard-sphere fluid is studied by a Monte Carlomolecular dynamics method for volumes ranging from 25V ₀ to 1.6V ₀ , whereV ₀ is the close-packed volume, and for system sizes from 108 to 4000 particles. TheN dependence of the equation of state is compared to the theoretical dependence given by Salsburg for theNPT ensemble, after correction for the ensemble difference, in order to obtain estimates for the thermodynamic limit. The observed values of the pressure are compared with both the [3/2] and the [2/3] Padé approximants to the virial series, using Kratky's value for the fifth virial coefficientB ₅ and choosingB ₆ andB ₇, to obtain a least-squares fit. The resulting values ofB ₆ andB ₇ lie within the uncertainties of the Ree-Hoover-Kratky Monte Carlo estimates for these virial coefficients. The values ofB ₈,B ₉, andB ₁₀ predicted by our optimal [3/2] approximant are also reported. Finally, the Monte Carlo-molecular dynamics equation of state is compared with a number of analytic expressions for the hard-sphere equation of state.Work supported by the Office of Basic Energy Sciences, U.S. Department of Energy.     

Amperometric bienzyme electrode for l-carnitine

An electrochemical sensor with two soluble enzymes allows assay of 0.1–10 mM, l- carnitine with an accuracy of 2%. The assay takes about 2 min. The first enzyme, carnitine dehydrogenase, catalyzes the oxidation of l-carnitine by NAD⁺. The NADH formed is oxidized by hexacyanoferrate(III) in a reaction catalyzed by diaphorase, and the hexacyanoferrate(II) produced is oxidized by electrolysis at 0.3 V. The sensor can be used for several days.     

REGULATION OF PROTOCHLOROPHYLL(IDE) LEVELS IN DARK-GROWN NON-DIVIDING Euglena—II. INFLUENCE OF UTILIZABLE SUBSTRATES AND INHIBITORS OF PROTEIN SYNTHESIS*

Dark-grown cells of Euglena gracilis var. bacillaris incubated on resting medium for 7 days lose half of their extractable and phototransformable protochlorophyll(ide) [Pchl(ide)]. The readily-utilized substrates glutamate and malate bring about a regeneration of both pools of Pchl(ide) to the levels found in growing cells, without causing cell division during the period of regeneration. Light does not cause a regeneration of total extractable Pchl(ide) to the levels found in growing cells, and the complete regeneration of phototransformable Pchl(ide) seen probably results from conversion of non-transformable Pchl(ide) to transformable Pchl(ide). Optimal glutamate, malate, and light in any combination are no better in causing phototransformable Pchl(ide) regeneration than any one treatment alone, indicating that the Pchl(ide) pool size is limited by other factors. The regeneration of phototransformable Pchl(ide) induced by light or substrates is insensitive to inhibitors of protein synthesis on 80 S cytoplasmic ribosomes (cycloheximide) or on 70 S chloroplast ribosomes (streptomycin). Cycloheximide, however, induces the regeneration of phototransformable Pchl(ide) in darkness in the absencc of externally-added substrates. Since cycloheximide is known to induce paramylum breakdown under the same conditions, it is likely that this process can provide internal substrates and/or reducing power for phototransformable Pchl(ide) regeneration. Possible mechanisms of regulation of formation of Pchl(ide)₆₃₅ in Euglena are discussed and compared with regulation of Pchl(ide)₆₅₀ in higher plants.     

A general solution of the diffusion equation for semiinfinite geometries

The solution of the time-dependent diffusion equation in a semiinfinite planar, cylindrical, or spherical geometry with common initial and asymptotic boundary conditions is considered. It is shown that this boundary value problem may be described by a single equation which involves only a first order spatial derivative and a half order time derivative. The replacement is exact in the planar and spherical geometry cases but approximate in the cylindrical case. This replacement permits the solution of the original boundary value problem to be written for any boundary condition at the origin. It also leads to a simple relationship between the boundary flux and the boundary intensive variable, which does not require a calculation of the intensive variable at all positions and times.     

Secure analysis of distributed chemical databases without data integration

We present a method for performing statistically valid linear regressions on the union of distributed chemical databases that preserves confidentiality of those databases. The method employs secure multi-party computation to share local sufficient statistics necessary to compute least squares estimators of regression coefficients, error variances and other quantities of interest. We illustrate our method with an example containing four companies' rather different databases.     

Gas Electron Diffraction and its Influence on the Solution of the Phase Problem in Crystal Structure Determination

We studied, and performed research for our Ph.D. degrees in the area of gas electron diffraction. Our mentor was Lawrence Brockway. a pioneer in this subject. At that time, research in gas electron diffraction was in its early stages of development. In 1941, the distinguished Peter Debye wrote a theoretical paper concerning gas electron diffraction which challenged ones capability to develop the necessary experimental equipment and to further advance the theoretical developments so as to greatly extend the science of gas electron diffraction. We carried these thoughts in mind when we joined the Naval Research Laboratory, where the opportunity to design and produce excellent equipment was readily available. In the course of pursuing this research area, one of the findings was the existence of non-negativity as a condition for the results of a diffraction experiment for gaseous substances. When we became interested in the field of crystal structure determination, the familiarity with non-negativity which was needed in the study of gases, led to a search for the necessary and sufficient condition for a Fourier series to be non-negative. The search was successful and has played an important part in crystal structure determination. Some early applications to complicated structures are described.