681 research outputs found
Statistical physics of cerebral embolization leading to stroke
We discuss the physics of embolic stroke using a minimal model of emboli
moving through the cerebral arteries. Our model of the blood flow network
consists of a bifurcating tree, into which we introduce particles (emboli) that
halt flow on reaching a node of similar size. Flow is weighted away from
blocked arteries, inducing an effective interaction between emboli. We justify
the form of the flow weighting using a steady flow (Poiseuille) analysis and a
more complicated nonlinear analysis. We discuss free flowing and heavily
congested limits and examine the transition from free flow to congestion using
numerics. The correlation time is found to increase significantly at a critical
value, and a finite size scaling is carried out. An order parameter for
non-equilibrium critical behavior is identified as the overlap of blockages'
flow shadows. Our work shows embolic stroke to be a feature of the cerebral
blood flow network on the verge of a phase transition.Comment: 11 pages, 11 figures. Major rewrite including improved justification
of the model and a finite size scalin
Rapid response of habitat structure and above-ground carbon storage to altered fire regimes in tropical savanna
Fire regimes across the globe have been altered through changes in land use,
land management, and climate conditions. Understanding how these modified fire
regimes impact vegetation structure and dynamics is essential for informed
biodiversity conservation and carbon management in savanna ecosystems. We
used a fire experiment at the Territory Wildlife Park (TWP), northern
Australia, to investigate the consequences of altered fire regimes for
vertical habitat structure and above-ground carbon storage. We mapped
vegetation three-dimensional (3-D) structure in high spatial resolution with
airborne lidar across 18 replicated 1 ha plots of varying fire frequency
and season treatments. We used lidar-derived canopy height and cover metrics
to extrapolate field-based measures of woody biomass to the full extent of
the experimental site (R2=0.82, RMSE = 7.35 t C ha−1) and
analysed differences in above-ground carbon storage and canopy structure among
treatments. Woody canopy cover and biomass were highest in the absence of
fire (76 % and 39.8 t C ha−1) and lowest in plots burnt late in
the dry season on a biennial basis (42 % and 18.2 t C ha−1).
Woody canopy vertical profiles differed among all six fire treatments, with
the greatest divergence in height classes <5 m. The magnitude of fire effects
on vegetation structure varied along the environmental gradient underpinning
the experiment, with less reduction in biomass in plots with deeper soils.
Our results highlight the large extent to which fire management can shape
woody structural patterns in savanna landscapes, even over time frames as
short as a decade. The structural profile changes shown here, and the
quantification of carbon reduction under late dry season burning, have
important implications for habitat conservation, carbon sequestration, and
emission reduction initiatives in the region.</p
A Sm(II)-mediated cascade approach to Dibenzoindolo[3,2-b]carbazoles:synthesis and evaluation
Previously unstudied dibenzoindolo[3,2-b]carbazoles have been prepared by two-directional, phase tag-assisted synthesis utilizing a connective-Pummerer cyclization and a SmI2-mediated tag cleavage-cyclization cascade. The use of a phase tag allows us to exploit unstable intermediates that would otherwise need to be avoided. The novel materials were characterized by X-ray, cyclic voltammetry, UV-vis spectroscopy, TGA, and DSC. Preliminary studies on the performance of OFET devices are also described
Constitutively Enhanced Lymphatic Pumping in the Upper Limbs of Women Who Later Develop Breast Cancer-Related Lymphedema.
BACKGROUND: It has previously been shown that the lymph drainage rate in both upper limbs is greater in women destined to develop breast cancer-related lymphedema (BCRL) than in those who do not develop BCRL, indicating a constitutive predisposition. We explored constitutive differences further by measuring the maximum lymphatic pump pressure (Ppump) and the rate of (99m)Tc-Nanocoll transport generated by the contractile upper limb lymphatics before and after breast cancer surgery in a group of women who were followed for 2 years to determine their eventual BCRL or non-BCRL status. METHODS AND RESULTS: Ppump and tracer transport rate were measured by lymphatic congestion lymphoscintigraphy in the ipsilateral upper limb in 26 women pre- and post-breast cancer surgery. BCRL occurred in 10/26 (38.5%) cases. Ppump in the women who later developed BCRL (40.0 ± 8.2 mmHg) was 1.7-fold higher than in those who did not develop BCRL (23.1 ± 10.8 mmHg, p = 0.001). Moreover, the rate of lymph tracer transport into the forearm was 2.2-fold greater in the women who later developed BCRL (p = 0.052). Surgery did not significantly reduce Ppump measured 21 weeks postsurgery, but impaired forearm tracer transport in pre-BCRL women by 58% (p = 0.047), although not in those who did not develop BCRL. CONCLUSIONS: Women destined to develop BCRL have higher pumping pressures and lymph transport, indicating harder-working lymphatics before cancer treatment. Axillary lymphatic damage from surgery appears to compromise lymph drainage in those women constitutively predisposed to higher lymphatic pressures and lymph transport
- …