High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters.

Laser light scattering systems with volume Bragg grating (VBG) filters, which act as spectral/angular filters, have often been used as a point measurement technique, with spatial resolution as low as a few hundred µm, defined by the beam waist. In this work, we demonstrate how VBG filters can be leveraged for spatially resolved measurements with several µm resolution over a few millimeters along the beam propagation axis. The rejection ring, as determined by the angular acceptance criteria of the filter, is derived analytically, and the use of the ring for 1D laser line rejection is explained. For the example cases presented,i.e., for a focused probe beam waist with a diameter of ∼150 µm, the rejection ring can provide resolution up to several millimeter length along the beam propagation axis for a 1D measurement, which is also tunable. Additionally, methods to further extend the measurable region are proposed and demonstrated, using a collimation lens with a different focal length or using multiple VBG filters. The latter case can minimize the scattering signal loss, without the tradeoff of the solid angle. Such use of multiple VBGs is to extend the measurable region along the beam axis, which differs from the commonly known application of multiple filters, to improve the suppression of elastic interferences. 1D rotational Raman and Thomson scattering measurements are carried out on pulsed and DC discharges to verify this method. The system features compactness, simple implementation, high throughput, and flexibility, to accommodate various experimental conditions.

Experimental and analytical evaluation of an active barium vapor notch filter functioning at 355 nm.

This work presents an experimental and theoretical study of the 6s21S0→6s6p3P10 (791 nm) and 5s5d3D2→6s5f3F20 (355 nm) transitions within a low vapor pressure barium vapor in the absence of a buffer gas. To the authors' knowledge, this is the first measurement of the latter absorption feature. The study is motivated by the development of an optically controlled atomic vapor notch filter functioning at the third harmonic of the commonly used Nd:YAG laser at 355 nm. The low-pressure environment within the vapor source has enabled a deeper understanding of barium vapor collisional and velocity changing properties with a simple pump-probe spectroscopy measurement. The results demonstrate depletion of the ground state and subsequent population of the 5s5d3D2 level. Most notably, the 5s5d3D2→6s5f3F20 transition displays a non-thermal, cusped absorption curve. An analysis of this line shape in the context of existing analytical collisional kernels is presented. Additionally, a six-level kinetic model of the low-lying energy levels, incorporating spatial diffusion and collisional and radiative transitions, is introduced and compared to the measured level populations for the barium ground state and excited 5s5d3D2 state.

Resolved rotation-vibration non-equilibrium with rotational VIPA-CARS.

Simultaneous rotational and vibrational temperatures are measured in an N2 plasma with rotational coherent anti-Stokes Raman scattering (CARS) resolved with a virtually imaged phased array (VIPA)-based spectrometer. A VIPA spectrally separates rotational transitions for each vibrational state, allowing vibrational populations to be directly measured. VIPA-CARS is shown to provide more accurate measurements of non-equilibrium temperatures than grating-resolved rotational CARS. The general characteristics, limitations, and potential uses of VIPA-CARS are discussed.

Site-Dependent Coordination Bonding in Self-Assembled Metal-Organic Networks.

The combination of organic linkers with metal atoms on top of inorganic substrates offers promising perspectives for functional electronic and magnetic nanoscale devices. Typically, coordination bonds between electron-rich end groups and transition-metal atoms lead to the self-assembly of metal-organic nanostructures, whose shape and electronic and magnetic properties crucially depend on the type of ligand. Here, we report on the site-selective bonding properties of Co atoms to the dichotomic dicyanoazobenzene molecule with its carbonitrile and diazo N-based moieties as possible ligands. Using low-temperature scanning tunneling microscopy (STM) and spectroscopy measurements, we resolve the formation of self-assembled metal-organic motifs. Cobalt atoms exhibit a clear spectroscopic fingerprint dependent on the different coordination site, which is further used to map their position, otherwise not clearly visible in the topographic STM images. Density functional theory corroborates the observed bonding patterns and evidences their coordinative nature.

Rhizoids and protonemata of characean algae: model cells for research on polarized growth and plant gravity sensing.

Gravitropically tip-growing rhizoids and protonemata of characean algae are well-established unicellular plant model systems for research on gravitropism. In recent years, considerable progress has been made in the understanding of the cellular and molecular mechanisms underlying gravity sensing and gravity-oriented growth. While in higher-plant statocytes the role of cytoskeletal elements, especially the actin cytoskeleton, in the mechanisms of gravity sensing is still enigmatic, there is clear evidence that in the characean cells actin is intimately involved in polarized growth, gravity sensing, and the gravitropic response mechanisms. The multiple functions of actin are orchestrated by a variety of actin-binding proteins which control actin polymerisation, regulate the dynamic remodelling of the actin filament architecture, and mediate the transport of vesicles and organelles. Actin and a steep gradient of cytoplasmic free calcium are crucial components of a feedback mechanism that controls polarized growth. Experiments performed in microgravity provided evidence that actomyosin is a key player for gravity sensing: it coordinates the position of statoliths and, upon a change in the cell's orientation, directs sedimenting statoliths to specific areas of the plasma membrane, where contact with membrane-bound gravisensor molecules elicits short gravitropic pathways. In rhizoids, gravitropic signalling leads to a local reduction of cytoplasmic free calcium and results in differential growth of the opposite subapical cell flanks. The negative gravitropic response of protonemata involves actin-dependent relocation of the calcium gradient and displacement of the centre of maximal growth towards the upper flank. On the basis of the results obtained from the gravitropic model cells, a similar fine-tuning function of the actomyosin system is discussed for the early steps of gravity sensing in higher-plant statocytes.

Antiviral phenylpropanoid glycosides from the medicinal plant Markhamia lutea.

Three new phenylpropanoid glycosides, named luteoside A (3), luteoside B (4), and luteoside C (5), were isolated together with the known compounds verbascoside (1) and isoverbascoside (2) from the roots of the medicinal plant Markhamia lutea. The structures of the new compounds were determined to be 1-O-(3, 4-dihydroxyphenyl)ethyl beta-D-apiofuranosyl(1-->2)-alpha-l-rhamnopyranosyl(1-->3)-4-O- caffeo yl-6-acetyl-beta-d-glucopyranoside, 1-O-(3,4-dihydroxyphenyl)ethyl beta-d-apiofuranosyl(1-->2)-alpha-l-rhamnopyranosyl(1-->3)-6-O- caffeo yl-beta-d-glucopyranoside, and 1-O-(3,4-dihydroxyphenyl)ethyl beta-D-apiofuranosyl(1-->2)-alpha-l-rhamnopyranosyl(1-->3)-6-O- ferulo yl-beta-d-glucopyranoside, respectively, on the basis of chemical and spectroscopic data. All five phenylpropanoid glycosides exhibited potent in vitro activity against respiratory syncytial virus.

Characterization of human endogenous retrovirus type K virus-like particles generated from recombinant baculoviruses.

The family of human endogenous retrovirus type K (HERV-K) comprises members with long open reading frames (ORF) for retroviral proteins. The existence of a biologically active provirus with replicative capacities has not yet been demonstrated. To confirm the assumption that HERV-K codes for the previously observed retrovirus-like particles (human teratocarcinoma-derived virus, HTDV) in human teratocarcinoma cells, we have constructed recombinant full-length HERV-K cDNA-based baculoviruses with gag, pro, pol, and env ORFs. Two viral constructs were used for infections of insect cells, one bearing 67 bp of the 5' untranslated region upstream of the 5' splice donor (SD) site and of the retroviral genes, the second omitting the SD sequence. For both recombinant viruses, indirect immunofluorescence and laser scan analyses revealed expression of HERV-K Gag protein. Electron microscopy studies demonstrated efficient production of virus-like particles (VLPs) at the cytoplasmic cell membranes. These VLPs are morphologically identical with the HTDV phenotype. In immunoelectron microscopy of ultrathin frozen sections, anti-HERV-K Gag antibodies specifically reacted with HERV-K VLPs. In Western blots, in addition to the 76-kDa precursor protein, the putative major core protein with an apparent molecular mass of 32 kDa exhibited predominant immunoreactivity with anti-Gag antiserum. In contrast, neither HERV-K Env nor cORF proteins could be detected due to inefficient mRNA splicing. Purified particles from insect cell culture supernatants tested in an ultrasensitive reverse transcriptase assay revealed weak polymerase activity. The data demonstrate that HERV-K codes for retroviral particles of the HTDV phenotype.

Expression of human endogenous retrovirus type K envelope glycoprotein in insect and mammalian cells.

The human endogenous retrovirus type K (HERV-K) family codes for the human teratocarcinoma-derived retrovirus (HTDV) particles. The existence of the envelope protein (ENV) of HERV-K encoded by the subgenomic env mRNA has not yet been demonstrated. To study the genetic requirements for successful expression of ENV, we have constructed a series of recombinant HERV-K env expression vectors for infection and transfection experiments in insect cells and mammalian cells, respectively. Six baculovirus constructs bearing full-length or truncated HERV-K env with or without homologous or heterologous signal peptides were used for infections of insect cells. All recombinant baculoviruses yielded ENV proteins with the expected molecular masses. The full-length 80- to 90-kDa HERV-K ENV protein including the cORF leader sequence was glycosylated in insect cells. In addition, the 14-kDa cORF protein was expressed due to splicing of the full-length env mRNA. The ENV precursor protein is not cleaved to the surface (SU) and transmembrane (TM) glycoproteins; it does not appear on the surface of infected insect cells and is not secreted into the medium. For ENV expression in COS cells, plasmid vectors harboring the cytomegalovirus immediate-early promoter/intron A element and the tissue plasminogen activator (t-PA) signal peptide or the homologous HERV-K signal peptide upstream of the env gene were employed. Glycosylated and uncleaved ENV was expressed as in GH teratocarcinoma cells but at higher levels. The heterologous t-PA signal sequence was instrumental for expression of HERV-K ENV on the cell surface. Hence, we have shown for the first time that the HERV-K env gene has the potential to be expressed as a full-length envelope protein with appropriate glycosylation. In addition, our data provide explanations for the lack of infectivity of HERV-K/HTDV particles.

HERV-K: the biologically most active human endogenous retrovirus family.

The human genome contains a wide variety of endogenous retrovirus-like sequences. The human endogenous retrovirus type K (HERV-K) family comprises 30-50 members per haploid genome in humans and is highly conserved in Old World monkeys and apes. Some proviruses are displaying open reading frames (ORF) with coding capacity for viral particles. HERV-K sequences most likely code for the previously described human teratocarcinoma-derived virus (HTDV) and correlated expression of HERV-K Gag has been demonstrated by immunoelectron microscopy studies. Protease, but not yet reverse transcriptase (RT), enzymatic activity was demonstrated for recombinant HERV-K proteins. However, an ultrasensitive RT assay revealed specific polymerase activity associated with the HTDV particles. HERV-K transcription is specifically regulated by viral long terminal repeats and RNA is expressed at low steady-state levels in a variety of human tissues and tumours. In teratocarcinoma cell lines, HERV-K is highly expressed in a complex pattern showing full-length as well as subgenomic envelope (env) and two alternatively spliced small transcripts. The doubly spliced 1.8-kb mRNA codes for cORF protein which resembles Rev of HIV-1 and is located in the nucleolus. In addition, the cORF sequence acts as a leader and is essential for effective expression of glycosylated HERV-K Env protein. Although HERV-K sequences code for all necessary retroviral proteins, infectious particles could not yet be demonstrated. The putative implication of HERV sequences in pathophysiological processes, for example, testicular malignancies, remains to be elucidated.