2,774 research outputs found
Cross Metathesis Assisted Solid-Phase Synthesis of Glycopeptoids
A solid-phase synthesis of glycopeptoids was explored through olefin cross metathesis (CM). Peptoids and sugar derivatives with appropriate olefin moieties were coupled in the presence of an olefin metathesis catalyst to afford glycopeptoids in good yields. This systematic solid-phase CM study can provide facile access to the molecular sources of glycopeptidomimetics and postchemical modifications on various molecular scaffolds
Recent development of antiSMASH and other computational approaches to mine secondary metabolite biosynthetic gene clusters
Many drugs are derived from small molecules produced by microorganisms and plants, so-called natural products. Natural products have diverse chemical structures, but the biosynthetic pathways producing those compounds are often organized as biosynthetic gene clusters (BGCs) and follow a highly conserved biosynthetic logic. This allows for the identification of core biosynthetic enzymes using genome mining strategies that are based on the sequence similarity of the involved enzymes/genes. However, mining for a variety of BGCs quickly approaches a complexity level where manual analyses are no longer possible and require the use of automated genome mining pipelines, such as the antiSMASH software. In this review, we discuss the principles underlying the predictions of antiSMASH and other tools and provide practical advice for their application. Furthermore, we discuss important caveats such as rule-based BGC detection, sequence and annotation quality and cluster boundary prediction, which all have to be considered while planning for, performing and analyzing the results of genome mining studies
Microlensing Detections of Planets in Binary Stellar Systems
We demonstrate that microlensing can be used for detecting planets in binary
stellar systems. This is possible because in the geometry of planetary binary
systems where the planet orbits one of the binary component and the other
binary star is located at a large distance, both planet and secondary companion
produce perturbations at a common region around the planet-hosting binary star
and thus the signatures of both planet and binary companion can be detected in
the light curves of high-magnification lensing events. We find that identifying
planets in binary systems is optimized when the secondary is located in a
certain range which depends on the type of the planet. The proposed method can
detect planets with masses down to one tenth of the Jupiter mass in binaries
with separations <~ 100 AU. These ranges of planet mass and binary separation
are not covered by other methods and thus microlensing would be able to make
the planetary binary sample richer.Comment: 5 pages, two figures in JPG forma
The First Comprehensive Photometric Study of the Algol-type System CL Aurigae
We present the first extensive photometric results of CL Aur from our BVRI
CCD photometry made on 22 nights from 2003 November through 2005 February.
Fifteen new timings of minimum light were obtained. During the past 104 years,
the orbital period has varied due to a periodic oscillation superposed on a
continuous period increase. The period and semi-amplitude of the oscillation
are about 21.6 yrs and 0.0133 d, respectively. This detail is interpreted as a
light-travel-time effect due to a low-luminosity K-type star gravitationally
bound to the CL Aur close system. Our photometric study indicates that CL Aur
is a relatively short-period Algol-type binary with values of q=0.602 and
i=88.2. Mass transfer from the secondary to the primary eclipsing
component is at least partly responsible for the observed secular period change
with a rate of dP/dt = +1.4 d yr. A cool spot model has
been calculated but we think that an alternative hot-spot model resulting from
a gas stream impact on the hot star is more reasonable despite two difficulties
with the explanation. Absolute dimensions of the eclipsing system are deduced
and its present state is compared with tracks for single star and conservative
close binary evolution. Finally, we examine the possible reconciliation of two
different calculations of the luminosity of the hot spot and a
re-interpretation of the secular term of the period variability.Comment: 26 pages, including 5 figures and 9 tables, accepted for publication
in A
Limits of Binaries That Can Be Characterized by Gravitational Microlensing
Due to the high efficiency of planet detections, current microlensing planet
searches focus on high-magnification events. High-magnification events are
sensitive to remote binary companions as well and thus a sample of
wide-separation binaries are expected to be collected as a byproduct. In this
paper, we show that characterizing binaries for a portion of this sample will
be difficult due to the degeneracy of the binary-lensing parameters. This
degeneracy arises because the perturbation induced by the binary companion is
well approximated by the Chang-Refsdal lensing for binaries with separations
greater than a certain limit. For binaries composed of equal mass lenses, we
find that the lens binarity can be noticed up to the separations of
times of the Einstein radius corresponding to the mass of each lens. Among
these binaries, however, we find that the lensing parameters can be determined
only for a portion of binaries with separations less than times of
the Einstein radius.Comment: 5 pages, 3 figures, 1 tabl
Photometric Properties of the Near-contact Binary GW Geminorum
New multiband CCD photometry is presented for the eclipsing binary GW Gem;
the light curves are the first ever compiled. Four new minimum timings
have been determined. Our analysis of eclipse timings observed during the past
79 years indicates a continuous period increase at a fractional rate of
+(1.20.1), in excellent agreement with the value
calculated from the Wilson-Devinney binary code. The new
light curves display an inverse O'Connell effect increasing toward longer
wavelengths. Hot and cool spot models are developed to describe these
variations but we prefer a cool spot on the secondary star. Our light-curve
synthesis reveals that GW Gem is in a semi-detached, but near-contact,
configuration. It appears to consist of a near-main-sequence primary star with
a spectral type of about A7 and an evolved early K-type secondary star that
completely fills its inner Roche lobe. Mass transfer from the secondary to the
primary component is responsible for the observed secular period change.Comment: 20 pages, including 5 figures and 6 tables, accepted for publication
in PAS
Perspective and Potential of Smart Optical Materials
The increasing requirements of hyperspectral imaging optics, electro/photo-chromic materials, negative refractive index metamaterial optics, and miniaturized optical components from microscale to quantum-scale optics have all contributed to new features and advancements in optics technology. Development of multifunctional capable optics has pushed the boundaries of optics into new fields that require new disciplines and materials to maximize the potential benefits. The purpose of this study is to understand and show the fundamental materials and fabrication technology for field-controlled spectrally active optics (referred to as smart optics) that are essential for future industrial, scientific, military, and space applications, such as membrane optics, light detection and ranging (LIDAR) filters, windows for sensors and probes, telescopes, spectroscopes, cameras, light valves, light switches, and flat-panel displays. The proposed smart optics are based on the Stark and Zeeman effects in materials tailored with quantum dot arrays and thin films made from readily polarizable materials via ferroelectricity or ferromagnetism. Bound excitonic states of organic crystals are also capable of optical adaptability, tunability, and reconfigurability. To show the benefits of smart optics, this paper reviews spectral characteristics of smart optical materials and device technology. Experiments testing the quantum-confined Stark effect, arising from rare earth element doping effects in semiconductors, and applied electric field effects on spectral and refractive index are discussed. Other bulk and dopant materials were also discovered to have the same aspect of shifts in spectrum and refractive index. Other efforts focus on materials for creating field-controlled spectrally smart active optics (FCSAO) on a selected spectral range. Surface plasmon polariton transmission of light through apertures is also discussed, along with potential applications. New breakthroughs in micro scale multiple zone plate optics as a micro convex lens are reviewed, along with the newly discovered pseudo-focal point not predicted with conventional optics modeling. Micron-sized solid state beam scanner chips for laser waveguides are reviewed as well
Ring-Closing Metathesis Approaches for the Solid-Phase Synthesis of Cyclic Peptoids
Cyclic peptoids were efficiently synthesized on a solid phase in high yields utilizing ring-closing metathesis (RCM). This method should be a valuable tool for easy access to cyclic peptoid libraries and various cyclic compounds
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