Moderate folate depletion increases plasma homocysteine and decreases lymphocyte DNA methylation in postmenopausal women

To determine the human folate requirement on the basis of changes in biochemical pathways, we studied the effect of controlled folate intakes on plasma homocysteine and lymphocyte DNA methylation and deoxynucleotide content in healthy postmenopausal women. Eight women (49-63 y of age) were housed in a metabolic unit and fed a low folate diet containing 56 microg/d of folate for 91 d. Folate intake was varied by supplementing 55-460 microg/d of folic acid (pteroylglutamic acid) to the diet to provide total folate intake periods of 5 wk at 56 microg/d, 4 wk at 111 microg/d and 3 wk at 286-516 microg/d. A subclinical folate deficiency with decreased plasma folate was created during the first two periods. This resulted in significantly elevated plasma homocysteine and urinary malondialdehyde, and lymphocyte DNA hypomethylation. The folate depletion also resulted in an increased ratio of dUTP/dTTP in mitogen-stimulated lymphocyte DNA and decreased lymphocyte NAD, changes suggesting misincorporation of uracil into DNA and increased DNA repair activity. The DNA hypomethylation was reversed with 286-516 microg/d of folate repletion, whereas the elevated homocysteine decreased with 516 but not 286 microg/d of folate. The results indicate that marginal folate deficiency may alter DNA composition and that the current RDA of 180 microg/d may not be sufficient to maintain low plasma homocysteine concentrations of some postmenopausal women.     

Stopping of crosslinking reaction in a PDMS polymer at the gel point

Summary A method has been developed to stop the crosslinking reaction of a polydimethylsiloxane system without disturbing the state of the sample. Oscillatory shear experiments on samples just before and just beyond the gelation point demonstrated the transition of the material from a viscoelastic liquid to a viscoelastic solid. At the gel point the loss modulus and the storage modulus were found to be identical over several decades of frequency and for temperatures ranging between -50°C and +180°C. Both moduli were proportional to the square root of the frequency.     

Thermal Rearrangements,XIII [1]. Thermal Isomerization of Exocyclic Allenes

The thermal isomerization of several exocyclic mono- and bis-allenes in a high-temperature flow system has been investigated. At 600°C vinylidenecyclobutane (10) rearranges cleanly to the allene dimer 1,2-bismethylenecyclobutane (12) by an allene-diene isomerization. The methylallene 16 behaves analogously (600°C), although the primary product 18 does not survive under the reaction conditions: the isolated cross-conjugated triene 20 is a product of a 1,5-hydrogen shift followed by an electrocylic ring-opening reaction. Whereas vinylidenecyclopentane (27) yields aromatic products only (800°C, toluene (36), benzene (38)), the five-ring 1,3-bisallene 30 isomerizes to the cyclopentene derivative 43 at 650°C. Vinylidenecyclohexane (46) affords only aromatic products again (760°C, o-xylene (57), 36, 38) and 1,3-bisvinylidenecyclohexane (49) isomerizes to the dienynes 60 and 61 by a series of hydrogen shifts at 550°C. On the other hand, the allene-diene isomerization is observed again, when a C–C bond is doubly activated by an allene and methylene group as in 52 or by two allene moieties as in 53: at 500°C the triene 63 and the exocyclic tetraene 65, respectively, are obtained in good yield.     

Accelerator mass spectrometry at the rehovot pelletron tandem: Measurements of abundances of cosmogenic radioisotopes and future prospects

The accelerator mass spectrometry system developed at the Rehovot 14UD Pelletron tandem laboratory has been used in measurements of abundances of cosmogenic nuclei. Measurements of ³⁶Cl concentrations in natural water samples from the Jordan River and Dead Sea Basin are presented in the framework of a ³⁶Cl budget analysis of the Dead Sea. The feasibility of ⁴¹Ca detection at concentrations ranging down to 1 × 10^?13 by tandem accelerator mass spectrometry has been demonstrated.     

Improved method of measuring loss and phase shifts in waveguide devices

The letter presents two novel methods, based on Fabry-Perot interference, for the characterisation of passive and active waveguide devices. Loss measurements have been made on passive devices using a distributed feedback laser as a frequency-tunable source. Simultaneous measurement of phase shift and loss are obtained for a phase modulator by using the electro-optic effect.     

Low-loss single-mode InP/InGaAsP waveguides grown by MOVPE

Losses as low as 0.4 ± 0.1 dB/cm for TE- and 0.65 ± 0.1 dB/ cm for TM-polarised light have been observed in tightly confined single-mode InP/lnGaAsP waveguides grown by MOVPE and processed using RIE. These are the lowest losses reported for InP-based waveguides. The structure could be used to make low-loss modulators for communications wavelengths.     

Location-aware mobile applications based on directory services

Location-aware applications are becoming increasingly attractive due to the widespread dissemination of wireless networks and the emergence of small and cheap locating technologies. We developed a location information server that simplifies and speeds up the development of these applications by offering a set of generic location retrieval and notification services to the application. The data model and the access protocols of these services are based on the X.500 directory service and the lightweight directory access protocol LDAP since these are becoming the standard attribute-value-pair retrieval mechanisms for Internet and Intranet environments. This approach establishes a smooth migration path from conventional to location-aware applications. The paper presents the location information server concepts, defines its directory data model and access services, and discusses the implementation options of the location information server. This revised version was published online in June 2006 with corrections to the Cover Date.