Cataloguing PL 4-manifolds by gem-complexity

We describe an algorithm to subdivide automatically a given set of PL n-manifolds (via coloured triangulations or, equivalently, via crystallizations) into classes whose elements are PL-homeomorphic. The algorithm, implemented in the case n=4, succeeds to solve completely the PL-homeomorphism problem among the catalogue of all closed connected PL 4-manifolds up to gem-complexity 8 (i.e., which admit a coloured triangulation with at most 18 4-simplices). Possible interactions with the (not completely known) relationship among different classification in TOP and DIFF=PL categories are also investigated. As a first consequence of the above PL classification, the non-existence of exotic PL 4-manifolds up to gem-complexity 8 is proved. Further applications of the tool are described, related to possible PL-recognition of different triangulations of the K3-surface.Comment: 25 pages, 5 figures. Improvements suggested by the refere

Computing Matveev's complexity via crystallization theory: the boundary case

The notion of Gem-Matveev complexity has been introduced within crystallization theory, as a combinatorial method to estimate Matveev's complexity of closed 3-manifolds; it yielded upper bounds for interesting classes of such manifolds. In this paper we extend the definition to the case of non-empty boundary and prove that for each compact irreducible and boundary-irreducible 3-manifold it coincides with the modified Heegaard complexity introduced by Cattabriga, Mulazzani and Vesnin. Moreover, via Gem-Matveev complexity, we obtain an estimation of Matveev's complexity for all Seifert 3-manifolds with base $\mathbb D^2$ and two exceptional fibers and, therefore, for all torus knot complements.Comment: 27 pages, 14 figure

High Resolution Near-Infrared Spectra of Protostars

We present new high resolution (R = 21,000) near-infrared (2 microns) spectroscopic observations of a sample of Class I and flat-spectrum protostellar objects in the rho Ophiuchi dark cloud. None of the five Class I spectra show CO v = 0 -- 2 absorption features, consistent with high K-band continuum veilings, 4 <= r_k <= 20 and fast stellar rotation, assuming that the underlying protostellar photospheres are of late spectral type, as is suggested by the low luminosities of most of these objects. Two of the flat-spectrum protostellar objects also show no absorption features and are likely to be highly veiled. The remaining two flat-spectrum sources show weak, broad absorptions which are consistent with an origin in quickly rotating (v sin i ~ 50 km / s) late-type stellar photospheres which are also strongly veiled, r_k = 3 - 4. These observations provide further evidence that: 1)-Class I sources are highly veiled at near-infrared wavelengths, confirming previous findings of lower resolution spectroscopic studies; and 2)- flat-spectrum protostars rotate more rapidly than classical T Tauri stars (Class II sources), supporting findings from a recent high resolution spectroscopic study of other flat-spectrum sources in this cloud. In addition our observations are consistent with the high rotation rates derived for two of the Class I protostellar objects in our sample from observations of variable hard X-ray emission obtained with the ASCA satellite. These observations suggest that certain Class I sources can rotate even more rapidly than flat-spectrum protostars, near breakup velocity.Comment: 16 pages including 2 tables and 2 figures (AASTeX 5.x) to be published in The Astronomical Journal July 200

Supercritical Carbon Dioxide Treatment Of Natural Biomaterials For Tissue Engineering Applications

The number of people requiring an organ transplant in the United States has increased considerably over the past 25 years, but the number of organ donations has stagnated; over 8,000 people now die annually while awaiting a transplant or become too sick to receive one. Tissue engineering (TE), the design and production of artificial tissues and organs in vitro, has been proposed to alleviate this problem. Though synthetic polymers offer tunable mechanical and biochemical properties, natural biomaterials have recently garnered attention in TE for their high degree of biocompatibility and ability to direct cell proliferation and constructive tissue remodeling. Yet scaffold processing remains challenging and a need for novel treatment and fabrication methods still exists. One underexplored method for creating TE scaffolds is treatment with supercritical fluids (SCFs). SCFs are appealing for treating biomaterials because of their desirable solvent properties; liquid-like densities and gas-like viscosities allow supercritical fluids to wet and penetrate matrices easily without damaging surface tension effects. Supercritical carbon dioxide (scCO2) is of particular interest. scCO2 is a non-toxic, non-flammable substance that is relatively inert and can be used to process biomaterials at physiologic temperatures and mild pressures. scCO2 treatment avoids organic solvents, does not leave cytotoxic residue, and has already been utilized in similar biomedical applications, including sterilization, pasteurization, biomolecule extraction, and removal of endotoxins, bioburden, and allergenic proteins. Supercritical CO2 has been used in foaming of synthetic polymer scaffolds, but it is almost completely unexplored in treatment of natural biomaterials for TE. In this dissertation, the potential of scCO2 in natural biomaterial TE is extensively explored. Two commonly-studied natural TE scaffold biomaterials were examined: a single-component biomaterial, type I collagen, and a multi-component biomaterial, extracellular matrix (ECM) obtained by decellularization of porcine aorta. Both biomaterials were studied at the fundamental and applied level. First, the chemical compatibility of collagen and liquid and scCO2 was assessed. Compatibility was determined based on changes in four biochemical properties: thermal stability, molecular weight, secondary structure, and overall appearance. For scCO2, no significant differences were observed, indicating chemical compatibility. Liquid CO2 treatment caused significant denaturing, though it was hypothesized that the apparent incompatibility may be a result of treatment conditions rather than total incompatibility. After chemical compatibility between collagen and scCO2 was established, scCO2 was applied to crosslinked collagen films to extract residual glutaraldehyde after crosslinking. After 1 hr of scCO2/ethanol treatment, over 95% of residual glutaraldehyde was removed, reducing the concentration below 1 ppm. Differential scanning calorimetry analysis showed a high degree of crosslinking and a denaturation temperature of about 63°C both before and after scCO2 treatment. Tensile testing did reveal a significant increase in both stiffness and tensile strength caused by scCO2 treatment, likely resulting from dehydration caused by the ethanol additive. However, this dehydration is preventable and less disruptive than heat-based removal of residual glutaraldehyde. Decellularized ECM is also commonly used as a TE scaffolds. Current decellularization methods often utilize chemical detergents, which are residually cytotoxic and can damage ECM composition and ultrastructure. scCO2 has been proposed as a decellularizing agent, but added ethanol severely dehydrates the matrix. The second half of this dissertation explores how scCO2 can decellularize a tissue without dehydrating it. To prevent dehydration, a novel presaturation method was developed where scCO2 and water are thoroughly mixed before treatment. Presaturation with water led to mass retention of over 99% in a model hydrogel and over 97% in porcine aorta during scCO2 treatment, compared to only 46% and 78%, respectively, when dry (pure) scCO2 was used, proving that dehydration during scCO2 treatment is easily prevented. Finally, scCO2 was used to decellularize porcine aorta. Contrary to a previous report, scCO2 alone was unable to achieve complete cell removal, even with a polar additive. However, when an SDS pretreatment step was used, the same scCO2 treatment completely decellularized porcine aorta as indicated by histology and DNA quantitation. Presaturation of scCO2 with water maintained the hydration state of the matrix, better maintaining the mechanical properties of the native tissue. This dissertation confirms the potential of supercritical CO2 as a processing method for naturally-derived biomaterial scaffolds. Further work can be performed to determine the efficacy of CO2 on different scaffold compositions and morphologies as well as decellularization of other tissue types. More complex treatments may also be possible, such as simultaneous sterilization and decellularization. These studies provide insight into the mechanisms and applications of scCO2 in TE and offer a springboard for impactful discoveries in the future

VIRIS: A Visual-Infrared Imaging System for the Lick Observatory 1-M Telescope

We describe a system in use at the Lick Observatory 1-m Nickel telescope for near-simultaneous imaging at optical and near-infrared wavelengths. The combined availability of a CCD and a NICMOS-3 camera makes the system well-suited for photometric monitoring from 0.5-2.2 microns of a variety of astrophysical objects. Our science program thus far has concentrated on studying variability trends in young stellar objects.Comment: 11 pages LaTex, 3 Postscript figure, Pub. Astr. Soc. Pac. 1998, in pres

Computing Matveev's complexity via crystallization theory: the orientable case

By means of a slight modification of the notion of GM-complexity introduced in [Casali, M.R., Topol. Its Appl., 144: 201-209, 2004], the present paper performs a graph-theoretical approach to the computation of (Matveev's) complexity for closed orientable 3-manifolds. In particular, the existing crystallization catalogue C-28 available in [Lins, S., Knots and Everything 5, World Scientific, Singapore, 1995] is used to obtain upper bounds for the complexity of closed orientable 3-manifolds triangulated by at most 28 tetrahedra. The experimental results actually coincide with the exact values of complexity, for all but three elements. Moreover, in the case of at most 26 tetrahedra, the exact value of the complexity is shown to be always directly computable via crystallization theory

A Companion Galaxy to the Post-Starburst Quasar UN J1025-0040

UN J1025-0040 is a quasar at z = 0.6344 that shows an extremely bright post starburst population of age ~ 400 Myr (Brotherton et al. 1999). Images of UN J1025-0040 show a nearly stellar object 4.2 arcseconds SSW of the quasar. We present imaging and spectroscopy that confirm that this object is a companion galaxy at redshift z = 0.6341. We estimate an age of ~ 800 Myr for the dominant stellar population in the companion. The companion appears to be interacting with the quasar host galaxy, and this interaction may have triggered both the starburst and the quasar activity in UN J1025-0040.Comment: 8 pages plus 4 figures (2 postscript, 2 jpg). Postscript version available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in the January 2000 issue of A

PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion

We present the results of adaptive-optics imaging of the z=0.2923 QSO PG 1700+518 in the J and H bands. The extension to the north of the QSO is clearly seen to be a discrete companion with a well-defined tidal tail, rather than a feature associated with the host galaxy of PG 1700+518 itself. On the other hand, an extension to the southwest of the QSO (seen best in deeper, but lower-resolution, optical images) does likely comprise tidal material from the host galaxy. The SED derived from images in J, H, and two non-standard optical bands indicates the presence of dust intermixed with the stellar component. We use our previously reported Keck spectrum of the companion, the SED found from the imaging data, and updated spectral-synthesis models to constrain the stellar populations in the companion and to redetermine the age of the starburst. While our best-fit age of 0.085 Gyr is nearly the same as our earlier determination, the fit of the new models is considerably better. This age is found to be remarkably robust with respect to different assumptions about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional figures in gif format. Postscript version including all figs. (424 kb) can be obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in ApJ. Letter