New wideband GaAs travelling-wave device: linear gate transistor

A new device called the linear the gate transistor (LGT) is described which promises in excess of 20 GHz flat-band performance in a single compact structure. The LGT is designed and modelled using a unique software package developed for all travelling-wave structures. Results from a prototype LGT are reported.     

Synthesis and Degradation of Hexamethylene Triperoxide Diamine (HMTD)

The synthesis and decomposition of hexamethylene triperoxide diamine (HMTD) were studied. Mechanisms were proposed based on isotopic labeling and mass spectral interpretation of both condensed phase products and head‐space products. Formation of HMTD from hexamine appeared to proceed from dissociated hexamine as evident from scrambling of the ¹⁵N label when synthesis was carried out with equal molar labeled/unlabeled hexamine. Decomposition of HMTD was considered with additives and in the presence and absence of moisture. In addition to mass spectral interpretation, density functional theory (DFT) was used to calculate energy differences of transition states and the entropies of intermediates along different possible decomposition pathways. HMTD is destabilized by water and citric acid making purification following initial synthesis essential in order to avoid unanticipated violent reaction.     

Factors Influencing Destruction of Triacetone Triperoxide (TATP)

Acid catalyzes the formation of triacetone triperoxide (TATP) from acetone and hydrogen peroxide, but acid also destroys TATP, and, under certain conditions, converts TATP to diacetone diperoxide (DADP). Addition of strong acids to TATP can cause an explosive reaction, while reaction with dilute acid reduces the decomposition rate so drastically that gentle destruction of TATP is impractical. However, combined use of dilute acid with slightly solvated TATP made gentle destruction of TATP feasible. Variables including acid type, concentration, solvent and ratios thereof have been explored, along with kinetics, in an attempt to provide a field‐safe technique for gently destroying this homemade primary explosive. The preferred method is moistening TATP with an alcoholic solution (aqueous methanol, ethanol, or iso‐propanol) followed by addition of 36 wt‐% hydrochloric acid. Preliminary experiments have shown the technique to be safe and effective for destruction of hexamethylene triperoxide diamine (HMTD), as well.     

Geranoyl-CoA carboxylase: a novel biotin-containing enzyme in plants

Geranoyl-CoA carboxylase (EC 6.4.1.4) is a biotin-containing enzyme previously described in two genera of bacteria. Here we report the presence of geranoyl-CoA carboxylase in kingdom Plantae. Geranoyl-CoA carboxylase was purified 180-fold from maize leaves. The enzyme has a biotin-containing subunit of 122 kDa. The pH optimum for activity is 8.3. The apparent Km values for the substrates geranoyl-CoA, bicarbonate, and ATP are 64 +/- 5 microM, 0. 58 +/- 0.04 mM, and 8.4 +/- 0.4 microM, respectively. Subcellular fractionations indicate that geranoyl-CoA carboxylase is located in plastids. Geranoyl-CoA carboxylase activity is ubiquitous in organs of monocots and dicots and varies with development. We postulate that geranoyl-CoA carboxylase plays an important role in isoprenoid catabolism in plants, in a pathway analogous to that shown in Psuedomonas sp. In plants, this catabolic pathway would require the interaction of at least three subcellular compartments (plastids, microbodies, and mitochondria) and two biotin-containing enzymes, geranoyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase.     

Phase retrieval and aberration correction in the presence of vortices in high-resolution transmission electron microscopy.

We discuss phase retrieval and the correction of images for aberrations, in particular defocus and spherical aberration, in high-resolution transmission electron microscopy. Non-interferometric phase retrieval requires at least two intensity measurements in different planes. Vortices in the phase may occur in the image plane or the other planes involved in the phase retrieval. We discuss the performance of various methods of phase retrieval in that case. After retrieval of the phase, the aberrations can be corrected in the Fraunhofer diffraction space (the wave function in the diffraction space is related to that in the image space by a Fourier transform). The aberration-corrected image is obtained from the aberration-corrected wave function in the diffraction plane by inverse Fourier transformation.     

Modulation of p27(Kip1) levels by the cyclin encoded by Kaposi's sarcoma-associated herpesvirus

DNA tumour viruses have evolved a number of mechanisms by which they deregulate normal cellular growth control. We have recently described the properties of a cyclin encoded by human herpesvirus 8 (also known as Kaposi's sarcoma-associated herpesvirus) which is able to resist the actions of p16(Ink4a), p21(Cip1) and p27(Kip1) cdk inhibitors. Here we investigate the mechanism involved in the subversion of a G1 blockade imposed by overexpression of p27(Kip1). We demonstrate that binding of K cyclin to cdk6 expands the substrate repertoire of this cdk to include a number of substrates phosphorylated by cyclin-cdk2 complexes but not cyclin D1-cdk6. Included amongst these substrates is p27(Kip1) which is phosphorylated on Thr187. Expression of K cyclin in mammalian cells leads to p27(Kip1) downregulation, this being consistent with previous studies indicating that phosphorylation of p27(Kip1) on Thr187 triggers its downregulation. K cyclin expression is not able to prevent a G1 arrest imposed by p27(Kip1) in which Thr187 is mutated to non-phosphorylatable Ala. These results imply that K cyclin is able to bypass a p27(Kip1)-imposed G1 arrest by facilitating phosphorylation and downregulation of p27(Kip1) to enable activation of endogenous cyclin-cdk2 complexes. The extension of the substrate repertoire of cdk6 by K cyclin is likely to contribute to the deregulation of cellular growth by this herpesvirus-encoded cyclin.     

Diltiazem and pentoxifylline determination in postmortem specimens

A 78-year-old woman was found dead in her basement. Qualitative screening of available postmortem specimens detected the presence of diltiazem and pentoxifylline. Quantitations were carried out by gas chromatography using nitrogen-phosphorus detection and confirmed by gas chromatography-mass spectrometry with the following results: blood, 0.59 mg/dL diltiazem and 0.63 mg/dL pentoxifylline; urine, 1.17 mg/dL diltiazem and 0.08 mg/dL pentoxifylline; bile, 0.40 mg/dL diltiazem and 0.22 mg/dL pentoxifylline; gastric contents, 0.28 mg/dL diltiazem and 0.02 mg/dL pentoxifylline. Both drugs were found qualitatively in formaline-fixed tissues.