16 research outputs found
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
Cancer recurrence times from a branching process model
As cancer advances, cells often spread from the primary tumor to other parts
of the body and form metastases. This is the main cause of cancer related
mortality. Here we investigate a conceptually simple model of metastasis
formation where metastatic lesions are initiated at a rate which depends on the
size of the primary tumor. The evolution of each metastasis is described as an
independent branching process. We assume that the primary tumor is resected at
a given size and study the earliest time at which any metastasis reaches a
minimal detectable size. The parameters of our model are estimated
independently for breast, colorectal, headneck, lung and prostate cancers. We
use these estimates to compare predictions from our model with values reported
in clinical literature. For some cancer types, we find a remarkably wide range
of resection sizes such that metastases are very likely to be present, but none
of them are detectable. Our model predicts that only very early resections can
prevent recurrence, and that small delays in the time of surgery can
significantly increase the recurrence probability.Comment: 26 pages, 9 figures, 4 table
Arabidopsis cyclin-dependent kinase gene CDKG;2 is involved in organogenic responses induced in vitro
The Arabidopsis CDKG;2 gene encodes a putative cyclin-dependent Ser/Thr protein kinase of unknown biological
function. This gene shows structural similarity to animal and human cyclin-dependent (PITSLRE) kinases.
This study used the homozygous knockout cdkg;2 mutant based on T-DNA insertional line SALK_090262 to study
the effect of mutation of the CDKG;2 gene on explant response and in vitro plant regeneration. For callus induction
and proliferation, hypocotyls and cotyledons of 3-day-old seedlings of cdkg;2 and A. thaliana ecotype Col-0 were cultured
on solid MS medium supplemented with 2,4-D (2 mg l-1). Organogenesis was induced after callus transfer on
MS + TDZ (0.5 mg l-1). The initiation time of callus and shoot induction differed between the mutant and control
cultures. Shoot regeneration after callus transfer on MS + TDZ was delayed in cdkg;2 (31 days versus 7 days in Col-
0). Shoots formed on callus derived from Col-0 hypocotyls but not on cotyledon-derived callus; in cdkg;2, shoots
developed on both callus types. Mutant shoots did not form roots, regenerants were dwarfed, and inflorescences had
small bud-like flowers with a reduced corolla and generative organs. Abnormalities observed during cdkg;2 organogenesis
suggest a role of CDKG;2 as a regulator of adventitious root initiation
Giant Splenic Artery Pseudoaneurysms: Two Case Reports and Cumulative Review of the Literature.
BACKGROUND: Giant splenic artery pseudoaneurysms (GSAPs) > 5 cm are a rare clinical entity. The aim of this study was to present our experience with 2 such patients successfully treated by coil embolization and surgery and review the pertinent literature. METHODS: A 58-year-old woman and 57-year-old man with a history of chronic pancreatitis were diagnosed with GSAP based on computed tomography (CT) angiography. The first patient had a 6-cm pseudoaneurysm, which was successfully treated with transcatheter coil embolization using a sandwich exclusion method. The second patient had two 7-cm lesions, which were successfully treated with distal pancreatectomy and splenectomy. RESULTS: Postembolization CT angiography at 12 months showed remaining calcified pseudocyst without evidence of pseudoaneurysm in the first patient. Both patients remained well and symptom-free at 12 months. CONCLUSIONS: Combined with the experience of the previous literature, we believe that management of GSAP should be tailored for each individual case depending on the location and number of pseudoaneurysms, the underlying etiology, and the patient's hemodynamic status. Embolization should be considered as the first-line treatment for clinically stable patients with GSAP, whereas GSAPs with a pseudocyst are best treated with surgery