244 research outputs found
Derivation of a Non-Local Interfacial Hamiltonian for Short-Ranged Wetting II: General Diagrammatic Structure
In our first paper, we showed how a non-local effective Hamiltionian for
short-ranged wetting may be derived from an underlying Landau-Ginzburg-Wilson
model. Here, we combine the Green's function method with standard perturbation
theory to determine the general diagrammatic form of the binding potential
functional beyond the double-parabola approximation for the
Landau-Ginzburg-Wilson bulk potential. The main influence of cubic and quartic
interactions is simply to alter the coefficients of the double parabola-like
zig-zag diagrams and also to introduce curvature and tube-interaction
corrections (also represented diagrammatically), which are of minor importance.
Non-locality generates effective long-ranged many-body interfacial interactions
due to the reflection of tube-like fluctuations from the wall. Alternative wall
boundary conditions (with a surface field and enhancement) and the diagrammatic
description of tricritical wetting are also discussed.Comment: (14 pages, 2 figures) Submitted J. Phys. Condens. Matte
Hydrogen bonding in acrylamide and its role in the scattering behavior of acrylamide-based block copolymers
Hydrogen bonding plays a role in the microphase separation behavior of many block copolymers, such as those used in lithography, where the stronger interactions due to H-bonding can lead to a smaller period for the self-assembled structures, allowing the production of higher resolution templates. However, current statistical thermodynamic models used in descriptions of microphase separation, such as the Flory-Huggins approach, do not take into account some important properties of hydrogen bonding, such as site specificity and cooperativity. In this combined theoretical and experimental study, a step is taken toward the development of a more complete theory of hydrogen bonding in polymers, using polyacrylamide as a model system. We begin by developing a set of association models to describe hydrogen bonding in amides. Both models with one association constant and two association constants are considered. This theory is used to fit IR spectroscopy data from acrylamide solutions in chloroform, thereby determining the model parameters. These parameters are then employed to calculate the scattering function of the disordered state of a diblock copolymer with one polyacrylamide block and one non-hydrogen-bonding block in the random phase approximation. It is then shown that the expression for the inverse scattering function with hydrogen bonding is the same as that without hydrogen bonding, but with the Flory-Huggins parameter Ï replaced by an effective value Ïeff=Ï+ÎŽÏHB(f), where the hydrogen-bonding contribution ÎŽÏHB depends on the volume fraction f of the hydrogen-bonding block. We find that models with two constants give better predictions of bond energy in the acrylamide dimer and more realistic asymptotic behavior of the association constants and ÎŽÏHB in the limit of high temperatures
3D wedge filling and 2D random-bond wetting
Fluids adsorbed in 3D wedges are shown to exhibit two types of continuous
interfacial unbinding corresponding to critical and tricritical filling
respectively. Analytic solution of an effective interfacial model based on the
transfer-matrix formalism allows us to obtain the asymptotic probability
distribution functions for the interfacial height when criticality and
tricriticality are approached. Generalised random walk arguments show that, for
systems with short-ranged forces, the critical singularities at these
transitions are related to 2D complete and critical wetting with random bond
disorder respectively.Comment: 7 pages, 3 figures, accepted for publication in Europhysics Letter
Crossover behavior and multi-step relaxation in a schematic model of the cut-off glass transition
We study a schematic mode-coupling model in which the ideal glass transition
is cut off by a decay of the quadratic coupling constant in the memory
function. (Such a decay, on a time scale tau_I, has been suggested as the
likely consequence of activated processes.) If this decay is complete, so that
only a linear coupling remains at late times, then the alpha relaxation shows a
temporal crossover from a relaxation typical of the unmodified schematic model
to a final strongly slower-than-exponential relaxation. This crossover, which
differs somewhat in form from previous schematic models of the cut-off glass
transition, resembles light-scattering experiments on colloidal systems, and
can exhibit a `slower-than-alpha' relaxation feature hinted at there. We also
consider what happens when a similar but incomplete decay occurs, so that a
significant level of quadratic coupling remains for t>>tau_I. In this case the
correlator acquires a third, weaker relaxation mode at intermediate times. This
empirically resembles the beta process seen in many molecular glass formers. It
disappears when the initial as well as the final quadratic coupling lies on the
liquid side of the glass transition, but remains present even when the final
coupling is only just inside the liquid (so that the alpha relaxation time is
finite, but too long to measure). Our results are suggestive of how, in a
cut-off glass, the underlying `ideal' glass transition predicted by
mode-coupling theory can remain detectable through qualitative features in
dynamics.Comment: 14 pages revtex inc 10 figs; submitted to pr
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The UK WTC 9/11 evacuation study: methodologies used in the elicitation and storage of human factors data
This paper describes the methodologies employed in the collection and storage of first-hand accounts of evacuation experiences derived from face-to-face interviews with evacuees from the World Trade Center (WTC) Twin Towers complex on 11 September 2001. In particular the paper describes the development of the High-rise Evacuation Evaluation Database (HEED). This is a flexible qualitative research tool which contains the full transcribed interview accounts and coded evacuee experiences extracted from those transcripts. The data and information captured and stored in the HEED database is not only unique, but it provides a means to address current and emerging issues relating to human factors associated with the evacuation of high-rise buildings
Prototyping of petalets for the Phase-II Upgrade of the silicon strip tracking detector of the ATLAS Experiment
In the high luminosity era of the Large Hadron Collider, the HL-LHC, the
instantaneous luminosity is expected to reach unprecedented values, resulting
in about 200 proton-proton interactions in a typical bunch crossing. To cope
with the resultant increase in occupancy, bandwidth and radiation damage, the
ATLAS Inner Detector will be replaced by an all-silicon system, the Inner
Tracker (ITk). The ITk consists of a silicon pixel and a strip detector and
exploits the concept of modularity. Prototyping and testing of various strip
detector components has been carried out. This paper presents the developments
and results obtained with reduced-size structures equivalent to those foreseen
to be used in the forward region of the silicon strip detector. Referred to as
petalets, these structures are built around a composite sandwich with embedded
cooling pipes and electrical tapes for routing the signals and power. Detector
modules built using electronic flex boards and silicon strip sensors are glued
on both the front and back side surfaces of the carbon structure. Details are
given on the assembly, testing and evaluation of several petalets. Measurement
results of both mechanical and electrical quantities are shown. Moreover, an
outlook is given for improved prototyping plans for large structures.Comment: 22 pages for submission for Journal of Instrumentatio
Alibava : A portable readout system for silicon microstrip sensors
A portable readout system for silicon microstrip sensors is currently being developed. This system uses a front-end readout chip, which was developed for the LHC experiments. The system will be used to investigate the main properties of this type of sensors and their future applications. The system is divided in two parts: a daughter board and a mother board. The first one is a small board which contains two readout chips and has fan-ins and sensor support to interface the sensors. The last one is intended to process the analogue data that comes from the readout chips and from external trigger signals, to control the whole system and to communicate with a PC via USB. The core of this board is a FPGA that controls the readout chips, a 10 bit ADC, an integrated TDC and an USB controller. This board also contains the analogue electronics to process the data that comes from the readout chips. There is also provision for an external trigger input (e.g. scintillator trigger) and a 'synchronised' trigger output for pulsing an external excitation source (e.g. laser system)
A double-sided, shield-less stave prototype for the ATLAS upgrade strip tracker for the high luminosity LHC
A detailed description of the integration structures for the barrel region of the silicon strips tracker of the ATLAS Phase-II upgrade for the upgrade of the Large Hadron Collider, the so-called High Luminosity LHC (HL-LHC), is presented. This paper focuses on one of the latest demonstrator prototypes recently assembled, with numerous unique features. It consists of a shortened, shield-less, and double sided stave, with two candidate power distributions implemented. Thermal and electrical performances of the prototype are presented, as well as a description of the assembly procedures and tools
A double-sided silicon micro-strip super-module for the ATLAS inner detector upgrade in the high-luminosity LHC
The ATLAS experiment is a general purpose detector aiming to fully exploit the discovery potential of the Large Hadron Collider (LHC) at CERN. It is foreseen that after several years of successful data-taking, the LHC physics programme will be extended in the so-called High-Luminosity LHC, where the instantaneous luminosity will be increased up to 5 Ă 1034 cmâ2 sâ1. For ATLAS, an upgrade scenario will imply the complete replacement of its internal tracker, as the existing detector will not provide the required performance due to the cumulated radiation damage and the increase in the detector occupancy. The current baseline layout for the new ATLAS tracker is an all-silicon-based detector, with pixel sensors in the inner layers and silicon micro-strip detectors at intermediate and outer radii. The super-module is an integration concept proposed for the strip region of the future ATLAS tracker, where double-sided stereo silicon micro-strip modules are assembled into a low-mass local support structure. An electrical super-module prototype for eight double-sided strip modules has been constructed. The aim is to exercise the multi-module readout chain and to investigate the noise performance of such a system. In this paper, the main components of the current super-module prototype are described and its electrical performance is presented in detail
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