33 research outputs found
Expansion in perfect groups
Let Ga be a subgroup of GL_d(Q) generated by a finite symmetric set S. For an
integer q, denote by Ga_q the subgroup of Ga consisting of the elements that
project to the unit element mod q. We prove that the Cayley graphs of Ga/Ga_q
with respect to the generating set S form a family of expanders when q ranges
over square-free integers with large prime divisors if and only if the
connected component of the Zariski-closure of Ga is perfect.Comment: 62 pages, no figures, revision based on referee's comments: new ideas
are explained in more details in the introduction, typos corrected, results
and proofs unchange
Generators and commutators in finite groups; abstract quotients of compact groups
Let N be a normal subgroup of a finite group G. We prove that under certain
(unavoidable) conditions the subgroup [N,G] is a product of commutators [N,y]
(with prescribed values of y from a given set Y) of length bounded by a
function of d(G) and |Y| only. This has several applications: 1. A new proof
that G^n is closed (and hence open) in any finitely generated profinite group
G. 2. A finitely generated abstract quotient of a compact Hausdorff group must
be finite. 3. Let G be a topologically finitely generated compact Hausdorff
group. Then G has a countably infinite abstract quotient if and only if G has
an infinite virtually abelian continuous quotient.Comment: This paper supersedes the preprint arXiv:0901.0244v2 by the first
author and answers the questions raised there. Latest version corrects
erroneous Lemma 4.30 and adds new Cor. 1.1
Effective in vivo and ex vivo gene transfer to intestinal mucosa by VSV-G-pseudotyped lentiviral vectors
<p>Abstract</p> <p>Background</p> <p>Gene transfer to the gastrointestinal (GI) mucosa is a therapeutic strategy which could prove particularly advantageous for treatment of various hereditary and acquired intestinal disorders, including inflammatory bowel disease (IBD), GI infections, and cancer.</p> <p>Methods</p> <p>We evaluated vesicular stomatitis virus glycoprotein envelope (VSV-G)-pseudotyped lentiviral vectors (LV) for efficacy of gene transfer to both murine rectosigmoid colon <it>in vivo </it>and human colon explants <it>ex vivo</it>. LV encoding beta-galactosidase (LV-β-Gal) or firefly-luciferase (LV-fLuc) reporter genes were administered by intrarectal instillation in mice, or applied topically for <it>ex vivo </it>transduction of human colorectal explant tissues from normal individuals. Macroscopic and histological evaluations were performed to assess any tissue damage or inflammation. Transduction efficiency and systemic biodistribution were evaluated by real-time quantitative PCR. LV-fLuc expression was evaluated by <it>ex vivo </it>bioluminescence imaging. LV-β-Gal expression and identity of transduced cell types were examined by histochemical and immunofluorescence staining.</p> <p>Results</p> <p>Imaging studies showed positive fLuc signals in murine distal colon; β-Gal-positive cells were found in both murine and human intestinal tissue. In the murine model, β-Gal-positive epithelial and lamina propria cells were found to express cytokeratin, CD45, and CD4. LV-transduced β-Gal-positive cells were also seen in human colorectal explants, consisting mainly of CD45, CD4, and CD11c-positive cells confined to the LP.</p> <p>Conclusions</p> <p>We have demonstrated the feasibility of LV-mediated gene transfer into colonic mucosa. We also identified differential patterns of mucosal gene transfer dependent on whether murine or human tissue was used. Within the limitations of the study, the LV did not appear to induce mucosal damage and were not distributed beyond the distal colon.</p
Demethylation of ferulic acid and feruloyl-arabinoxylan by microbial cell extracts
25 ref. DOI:10.1006/fstl.2001.0856International audienc
Kinetics of the Sphere-to-Rod like Micelle Transition in a Pluronic Triblock Copolymer
The kinetics of the sphere-to-rod transition was studied
in aqueous
micelle solutions of triblock copolymer poly(ethylene oxide)–poly(propylene
oxide)–poly(ethylene oxide) pluronic P103 (PEO<sub>17</sub>PPO<sub>60</sub>PEO<sub>17</sub>). This transition was triggered
by a temperature jump from the sphere phase to the rod phase and monitored
with dynamic light scattering. The combination of the scattering intensity
and the hydrodynamic radius were used to show that the micelles grow
steadily as rods throughout the growth process. The transition was
found to exhibit a single exponential behavior even in the case of
large deviations from equilibrium. The linear increase in the decay
rate with increasing copolymer concentration shows that the transition
is dominated by a mechanism involving fusion and fragmentation of
proper micelles. The decays of the sphere-to-rod transition were simulated
for two pathways: random fusion fragmentation and successive addition
of spherical micelles to rods. We show that micelle growth most likely
occurs via random fusion-fragmentation. The second order rate constant
for fusion and the fragmentation rate are calculated for the case
of random fusion-fragmentation
NOTE ON THE GONALITY OF ABSTRACT MODULAR CURVES
Abstract. Let S be a curve over an algebraically closed field k of characteristic p ≥ 0. To any family ρ of n-dimensional Fℓ-linear representations: ρℓ: π1(S) → GLn(Fℓ), ℓ: prime (ℓ ≫ 0), one can associate ‘abstract modular curves ’ Sρ,1(ℓ) and Sρ(ℓ) which, in this setting, are the modular analogues of the classical modular curves Y1(ℓ) and Y (ℓ). The main result of this paper is that, under some technical assumptions, the gonality of Sρ(ℓ) goes to + ∞ with ℓ. These technical assumptions are satisfied by Fℓ-linear representations arising from the action of π1(S) on the étale cohomology groups with coefficients in Fℓ of the geometric generic fiber of a smooth proper scheme over S. From this, we deduce a new and purely algebraic proof of the fact that the gonality of Y1(ℓ) goes to + ∞ with ℓ
Reflections on concrete buildings
In the last few years there have been many constructions and characterizations of finite groups acting chamber-transitively on finite building-like geometries. A number o