283 research outputs found
From Car Parking to Protein Adsorption: An Overview of Sequential Adsorption Processes
The adsorption or adhesion of large particles (proteins, colloids, cells,
>...) at the liquid-solid interface plays an important role in many diverse
applications. Despite the apparent complexity of the process, two features are
particularly important: 1) the adsorption is often irreversible on experimental
time scales and 2) the adsorption rate is limited by geometric blockage from
previously adsorbed particles. A coarse-grained description that encompasses
these two properties is provided by sequential adsorption models whose simplest
example is the random sequential adsorption (RSA) process. In this article, we
review the theoretical formalism and tools that allow the systematic study of
kinetic and structural aspects of these sequential adsorption models. We also
show how the reference RSA model may be generalized to account for a variety of
experimental features including particle anisotropy, polydispersity, bulk
diffusive transport, gravitational effects, surface-induced conformational and
orientational change, desorption, and multilayer formation. In all cases, the
significant theoretical results are presented and their accuracy (compared to
computer simulation) and applicability (compared to experiment) are discussed.Comment: 51 pages, 18 Figures, to appear in a special volume entitled
"Adhesion of Submicron Particles on Solid Surfaces" of Colloids and Surfaces
A, guest-edited by V. Privman.to appear in a special volume entitle
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Brain metastases in osteosarcoma: incidence, clinical and neuroradiological findings and management options.
Brain metastasis is uncommon in osteosarcoma, but this may be changing with prolonged patient survival in the modern chemotherapy era. We present 5 patients with brain metastases out of 39 with lung metastasis (13%) in a total of 87 osteosarcoma patients. The clinical manifestations of brain metastases were catastrophic: massive hemorrhage in 2 and status epilepticus in 3. Metastases were single or multiple, and some were osteoblastic. Surgical intervention in 2 cases resulted in dramatic, though transient, clinical improvement. We advocate periodic neuroradiology screening in osteosarcoma patients with lung metastases, for early detection of brain involvement
Random Fan-Out State Induced by Site-Random Interlayer Couplings
We study the low-temperature properties of a classical Heisenberg model with
site-random interlayer couplings on the cubic lattice. This model is introduced
as a simplified effective model of Sr(FeMn)O, which was
recently synthesized. In this material, when , and
mixed ordering is observed by neutron diffraction measurements. By
Monte Carlo simulations, we find an exotic bulk spin structure that explains
the experimentally obtained results. We name this spin structure the "random
fan-out state". The mean-field calculations provide an intuitive understanding
of this phase being induced by the site-random interlayer couplings. Since
Rietveld analysis assuming the random fan-out state agrees well with the
neutron diffraction pattern of Sr(FeMn)O, we conclude that
the random fan-out state is reasonable for the spin-ordering pattern of
Sr(FeMn)O at the low-temperature phase.Comment: 13 pages, 12 figure
Gifted and talented education: The English policy highway at a crossroads?
Copyright © 2013 by Sage Publications. This is the author's accepted manuscript. The final published article is available from the link below.In 1999, the British government launched an education program for gifted and talented pupils as part of its Excellence in Cities initiative (EiC) that was initially designed to raise the educational achievement of very able pupils in state-maintained secondary schools in inner-city areas. Although some activities targeting gifted children had already been initiated by various voluntary organizations over several previous decades, this was the first time that the topic of improved provision for these pupils had been placed firmly within the national agenda. This article provides the background to the English gifted and talented policy “highway” and an overview of what was expected of schools. How practitioners responded to the policy, their beliefs and attitudes toward identifying gifted and talented pupils, and the opportunities and challenges that arose along the way to the current crossroads are explored. The need to empower teachers to feel more confident in classroom provisions for gifted and talented pupils is identified along with the potentially pivotal role of action research and “pupil voice” in the process of continued professional development and support
Field-induced evolution of magnetic ordering in the quantum spin system (CuBr)Sr<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> with a ⅓ magnetization plateau
The field-induced evolution of the magnetic ordering in (CuBr)Sr<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> with a 1/3 magnetization plateau has been investigated by neutron diffraction under magnetic fields up to 10 T. With an increasing magnetic field, the zero-field helical antiferromagnetic (AFM) phase, AF1, with κ = [0 3/8 1/2] is replaced by a simple ferromagnetic phase with κ = [0 0 0], the formation of which is, however, retarded by the appearance of a second AFM, AF2, with κ = [0 1/3 ∼0.46]. Upon further increasing of the magnetic field, the AF2 phase disappears and only the ferromagnetic phase persists. The results clearly show that the magnetization plateau, induced by the competition between field-induced ferromagnetic, F, and AF2 phases, is coincidentally situated at M = 1/3 MS of the dc magnetization curve. The AF1 and AF2 phases have strongly differing magnetic propagation vectors and are therefore not directly related
Dust Devil Tracks
Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth’s surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ∼1 m and ∼1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550–850 nm on Mars and around 0.5 % in the wavelength range from 300–1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns
Influência das coletas sistemáticas e parciais na seleção de codornas por meio de curvas de probabilidade de postura
Scaphoid Waist Internal Fixation for Fractures Trial (SWIFFT) protocol : a pragmatic multi-centre randomised controlled trial of cast treatment versus surgical fixation for the treatment of bi-cortical, minimally displaced fractures of the scaphoid waist in adults
BACKGROUND: A scaphoid fracture is the most common type of carpal fracture affecting young active people. The optimal management of this fracture is uncertain. When treated with a cast, 88 to 90 % of these fractures unite; however, for the remaining 10-12 % the non-union almost invariably leads to arthritis. The alternative is surgery to fix the scaphoid with a screw at the outset. METHODS/DESIGN: We will conduct a randomised controlled trial (RCT) of 438 adult patients with a "clear" and "bicortical" scaphoid waist fracture on plain radiographs to evaluate the clinical effectiveness and cost-effectiveness of plaster cast treatment (with fixation of those that fail to unite) versus early surgical fixation. The plaster cast treatment will be immobilisation in a below elbow cast for 6 to 10 weeks followed by mobilisation. If non-union is confirmed on plain radiographs and/or Computerised Tomogram at 6 to 12 weeks, then urgent surgical fixation will be performed. This is being compared with immediate surgical fixation with surgeons using their preferred technique and implant. These treatments will be undertaken in trauma units across the United Kingdom. The primary outcome and end-point will be the Patient Rated Wrist Evaluation (a patient self-reported assessment of wrist pain and function) at 52 weeks and also measured at 6, 12, 26 weeks and 5 years. Secondary outcomes include an assessment of radiological union of the fracture; quality of life; recovery of wrist range and strength; and complications. We will also qualitatively investigate patient experiences of their treatment. DISCUSSION: Scaphoid fractures are an important public health problem as they predominantly affect young active individuals in the more productive working years of their lives. Non-union, if untreated, can lead to arthritis which can disable patients at a very young age. There is a rapidly increasing trend for immediate surgical fixation of these fractures but there is insufficient evidence from existing RCTs to support this. The SWIFFT Trial is a rigorously designed and adequately powered study which aims to contribute to the evidence-base to inform clinical decisions for the treatment of this common fracture in adults. TRIAL REGISTRATION: The trial is registered with the International Standard Randomised Controlled Trial Register ( ISRCTN67901257 ). Date registration assigned was 13/02/2013
Impact of phase II trials with progression-free survival as end-points on survival-based phase III studies in patients with anaplastic gliomas
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