Galaxy threshing and the origin of ultra-compact dwarf galaxies in the Fornax cluster

A recent all-object spectroscopic survey centred on the Fornax cluster of galaxies has discovered a population of subluminous and extremely compact members, called 'ultra-compact dwarf' (UCD) galaxies. In order to clarify the origin of these objects, we have used self-consistent numerical simulations to study the dynamical evolution a nucleated dwarf galaxy would undergo if orbiting the centre of the Fornax cluster and suffering from its strong tidal gravitational field. We find that the outer stellar components of a nucleated dwarf are removed by the strong tidal field of the cluster, whereas the nucleus manages to survive as a result of its initially compact nature. The developed naked nucleus is found to have physical properties (e. g. size and mass) similar to those observed for UCDs. We also find that although this formation process does not have a strong dependence on the initial total luminosity of the nucleated dwarf, it does depend on the radial density profile of the dark halo in the sense that UCDs are less likely to be formed from dwarfs embedded in dark matter haloes with central 'cuspy' density profiles. Our simulations also suggest that very massive and compact stellar systems can be rapidly and efficiently formed in the central regions of dwarfs through the merging of smaller star clusters. We provide some theoretical predictions on the total number and radial number density profile of UCDs in a cluster and their dependencies on cluster masses.

Galaxy threshing and ultra-compact dwarfs in the Fornax cluster

We have discovered a new type of galaxy in the Fornax Cluster: 'ultra-compact' dwarfs (UCDs). The UCDs are unresolved in ground-based imaging and have spectra typical of old stellar systems. Although the UCDs resemble overgrown globular clusters, based on VLT UVES echelle spectroscopy, they appear to be dynamically distinct systems with higher internal velocity dispersions and M/L ratios for a given luminosity than Milky Way or M31 globulars. Our preferred explanation for their origin is that they are the remnant nuclei of dwarf elliptical galaxies which have been tidally stripped, or 'threshed' by repeated encounters with the central cluster galaxy, NGC1399. If correct, then tidal stripping of nucleated dwarfs to form UCDs may, over a Hubble time, be an important source of the plentiful globular cluster population in the halo of NGC1399, and, by implication, other cD galaxies. In this picture, the dwarf elliptical halo contents, up to 99% of the original dwarf luminosity, contribute a significant fraction of the populations of intergalactic stars, globulars, and gas in galaxy clusters.

Microanalysis of epitaxially grown diamond tip array

Electron backscattering diffraction has been applied on polycrystalline diamond films grown using microwave plasma assisted chemical vapour deposition on silicon substrate, in order to provide a map of the individual diamond grains, grain boundary, and the crystal orientation of discrete crystallites. The nucleation rate and orientation are strongly affected by using a voltage bias on the substrate to influence and enhance the nucleation process, the bias enhanced nucleation process. In this work, the diamond surface is mapped using electron backscattering diffraction, then a layer of a few microns is ion milled away exposing a lower layer for analysis and so on. This then permits a three dimensions reconstruction of the film texture.

Reducing the height of a circular array of monopoles using top hats and dielectric coatings

Using a Radial Guide Field Matching Method, an investigation is performed into reducing the height of an electronically steered circular array of monopole antennas composed of a central active element surrounded by passive elements being either short- or open-circuited. It is shown that a considerable height reduction can be achieved using top hats attached to monopoles ends and by applying dielectric coating underneath the top hats. The trade-off in achieving height reduction is narrower impedance bandwidth.

Improvement of compact terminal antenna performance by incorporating open-end slots in ground plane

This letter describes a new idea of increasing operational bandwidth of a compact planar inverted F antenna (PIFA) by introducing open-end slots in the ground plane under the radiating patch. The slots are not in the way of active modules of a wireless transceiver and thus the proposed antenna size reduction method is attractive from the point of view of practical implementation.

Super-fast scanning technique for phased array weather radar aplications

The authors present a super-fast scanning (SFS) technique for phased array weather radar applications. The fast scanning feature of the SFS technique is described and its drawbacks identified. Techniques which combat these drawbacks are also presented. A concept design phased array radar system (CDPAR) is used as a benchmark to compare the performance of a conventional scanning phased array radar system with the SFS technique. It is shown that the SFS technique, in association with suitable waveform processing, can realise four times the scanning speed and achieve similar accuracy compared to the conventional phased array benchmark.

Functional analysis of the a-defensin disulfide array in mouse cryptdin-4

The alpha-defensin antimicrobial peptide family is defined by a unique tridisulfide array. To test whether this invariant structural feature determines alpha-defensin bactericidal activity, mouse cryptdin-4 (Crp4) tertiary structure was disrupted by pairs of site-directed Ala for Cys substitutions. In a series of Crp4 disulfide variants whose cysteine connectivities were confirmed using NMR spectroscopy and mass spectrometry, mutagenesis did not induce loss of function. To the contrary, the in vitro bactericidal activities of several Crp4 disulfide variants were equivalent to or greater than those of native Crp4. Mouse Paneth cell alpha-defensins require the proteolytic activation of precursors by matrix metalloproteinase-7 (MMP-7), prompting an analysis of the relative sensitivities of native and mutant Crp4 and proCrp4 molecules to degradation by MMP-7. Although native Crp4 and the alpha-defensin moiety of proCrp4 resisted proteolysis completely, all disulfide variants were degraded extensively by MMP-7. Crp4 bactericidal activity was eliminated by MMP-7 cleavage. Thus, rather than determining alpha-defensin bactericidal activity, the Crp4 disulfide arrangement confers essential protection from degradation by this critical activating proteinase.

Ultra-compact dwarf galaxies in galaxy clusters

We review the evidence that the ultra-compact dwarf (UCD) galaxies we recently discovered in the Fornax Cluster form a new, previously unknown class of galaxies and we discuss possible scenarios for their formation. We then present recent results that UCDs are also present in the Virgo Cluster, and that there is a much larger than expected population of fainter UCDs in the Fornax Cluster. The size and properties of this population may lead us to revise our original 'galaxy threshing' hypothesis for the formation of UCDs.

The Hi content of compact groups of galaxies

The Hi content of Hickson Compact Groups in the southern hemisphere is measured using data from the Hi Parkes All-Sky Survey (HIPASS), and dedicated observations using the narrow band filter on the Multibeam instrument on the Parkes telescope. The expected Hi mass of these groups was estimated using the luminosity, diameter, and morphological types of the member galaxies, calibrated from published data. Taking careful account of non-detection limits, the results show that the compact group population that has been detected by these observations has an Hi content similar to that of galaxies in the reference field sample. The upper limits for the undetected groups lie within the normal range; improvement of these limits will require a large increase in sensitivity.

Compact tunable microfluidic interferometer

We demonstrate a compact tunable filter based on a novel microfluidic single beam Mach-Zehnder interferometer. The optical path difference occurs during propagation across a fluid-air interface ( meniscus), the inherent mobility of which provides tunability. Optical losses are minimized by optimizing the meniscus shape through surface treatment. Optical spectra are compared to a 3D beam propagation method simulations and good agreement is found. Tunability, low insertion loss and strength of the resonance are well reproduced. The device performance displays a resonance depth of - 28 dB and insertion loss maintained at - 4 dB. (C) 2004 Optical Society of America.

Optofluidics enables compact tunable interferometer

An optofluidic interferometer - in which a beam propagates across an interface between fluid and air - modulates at high extinction ratios and is only microns in size.

Investigations into a wideband spatial beamformer employing a rectangular array of planar monopoles

This paper presents a rectangular array antenna with a suitable signal-processing algorithm that is able to steer the beam in azimuth over a wide frequency band. In the previous approach, which was reported in the literature, an inverse discrete Fourier transform technique was proposed for obtaining the signal weighting coefficients. This approach was demonstrated for large arrays in which the physical parameters of the antenna elements were not considered. In this paper, a modified signal-weighting algorithm that works for arbitrary-size arrays is described. Its validity is demonstrated in examples of moderate-size arrays with real antenna elements. It is shown that in some cases, the original beam-forming algorithm fails, while the new algorithm is able to form the desired radiation pattern over a wide frequency band. The performance of the new algorithm is assessed for two cases when the mutual coupling between array elements is both neglected and taken into account.

Combating interference in an indoor wireless-communication system using a phased-array antenna with switched-beam elements

A phased-array antenna with switched-beam elements used to combat interference in an indoor wireless communication system is described. The array uses I-bit phase shifters applied to its elements in order to point its main beam in a desired direction and internal switching of elements in order to form nulls towards interference. The array's capability of suppressing interference is verified by studying its radiation patterns and by performing interference-rejection experiments in an indoor multipath environment. (c) 2005 Wiley Periodicals, Inc.

Practical dual-helical antenna array for diversity/MIMO receiving antennas on mobile handsets

A practical, small-size, dual-helical antenna array mounted on a mobile handset model is designed for use as diversity/MIMO receiving antennas. The array is rigorously studied with respect to its diversity performance and the achievable channel capacity. It is found that a very low correlation coefficient, a high diversity gain, an equal-mean branch SNR, and a relatively matched input impedance can be achieved at the same time. It is shown that, at a remarkably small antenna separation (similar to 0.05 lambda), the signal correlation can be reduced to nearly zero, an almost ideal independent operation of the diversity antennas. The increase in MIMO channel capacity is 100% over a single antenna system. Both measured and simulation results are presented.

Linewidth reduction in a large-smile laser diode array

We present theory and simulations for a spectral narrowing scheme for laser diode arrays (LDAs) that employs optical feedback from a diffraction grating. We calculate the effect of the so-called smile of the LDA and show that it is possible to reduce the effect by using a cylindrical lens set at an angle to the beam. The scheme is implemented on a 19-element LDA with smile of 7.6 mu m and yields frequency narrowing from a free-running width of 2 to 0.15 nm. The experimental results are in good agreement with the theory. (c) 2005 Optical Society of America.