Abstract: The stability of Newtonian and Non-Newtonian extending films under local or global heating or cooling conditions are considered. The thickness-averaged mass, momentum and energy equations with convective and radiative heat transfer are derived, both for Newtonian and non-Newtonian fluids (Maxwell, PTT and Giesekus models considered). The stability of the system is explored using either eigenvalue analysis or transient simulations. The results showed that the influence of heating and cooling on stability strongly depends on the magnitude of the Peclet number. Examples of stabilization or destabilization of heating or cooling are shown for Pe
Abstract: In this work, we study the impact of dynamically changing link slowdowns on the stability properties of packetswitched networks under the Adversarial Queueing Theory framework. Especially, we consider the Adversarial, Quasi-Static Slowdown Queueing Theory model, where each link slowdown may take on values in the two-valued set of integers {1, D} with D > 1 which remain fixed for a long time, under a (w, p)-adversary. In this framework, we present an innovative systematic construction for the estimation of adversarial injection rate lower bounds, which, if exceeded, cause instability in networks that use the LIS (Longest-in- System) protocol for contention-resolution. In addition, we show that a network that uses the LIS protocol for contention-resolution may result in dropping its instability bound at injection rates p > 0 when the network size and the high slowdown D take large values. This is the best ever known instability lower bound for LIS networks.
Abstract: The present research was focused to investigate the
role of investment in the course of economic growth with reference to
Pakistan. The study analyzed the role of the public and private
investment and impact of the political and macroeconomic
uncertainty on economic growth of Pakistan by using the vector
autoregressive approach (VAR). In long-run both public and private
investment showed a positive impact on economic growth but the
growth was largely driven by private investment as compared to
public investment. Government consumption expenditure, economic
uncertainty and political instability hampered the economic growth of
Pakistan. In short-run the private investment positively influences the
growth but there was negative and insignificant effect of the public
investment and government consumption expenditure on the growth.
There was a positive relationship found between economic
uncertainty (proxy for inflation) and GDP in short run.
Abstract: The integral form of equations of motion of composite
beams subjected to varying time loads are discretized using a
developed finite element model. The model consists of a straight five
node twenty-two degrees of freedom beam element. The stability
analysis of the beams is studied by solving the matrix form
characteristic equations of the system. The principle of virtual work
and the first order shear deformation theory are employed to analyze
the beams with large deformation and small strains. The regions of
dynamic instability of the beam are determined by solving the
obtained Mathieu form of differential equations. The effects of nonconservative
loads, shear stiffness, and damping parameters on
stability and response of the beams are examined. Several numerical
calculations are presented to compare the results with data reported
by other researchers.
Abstract: Shear-layer instabilities of a pulsed stack-issued
transverse jet were studied experimentally in a wind tunnel. Jet
pulsations were induced by means of acoustic excitation. Streak
pictures of the smoke-flow patterns illuminated by the laser-light sheet
in the median plane were recorded with a high-speed digital camera.
Instantaneous velocities of the shear-layer instabilities in the flow were
digitized by a hot-wire anemometer. By analyzing the streak pictures
of the smoke-flow visualization, three characteristic flow modes,
synchronized flapping jet, transition, and synchronized shear-layer
vortices, are identified in the shear layer of the pulsed stack-issued
transverse jet at various excitation Strouhal numbers. The shear-layer
instabilities of the pulsed stack-issued transverse jet are synchronized
by acoustic excitation except for transition mode. In transition flow
mode, the shear-layer vortices would exhibit a frequency that would be
twice as great as the acoustic excitation frequency.
Abstract: The structural stability of the model of a nonelectroneutral current sheath is investigated. The stationary model of a current sheath represents the system of four connected nonlinear differential first-order equations and thus they should manifest structural instability property, i.e. sensitivity to the infinitesimal changes of parameters and starting conditions. Domains of existence of the solutions of current sheath type are found. Those solutions of the current sheath type are realized only in some regions of sevendimensional space of parameters of the problem. The phase volume of those regions is small in comparison with the whole phase volume of the definition range of those parameters. It is shown that the offered model of a nonelectroneutral current sheath is applicable for theoretical interpretation of the bifurcational current sheaths observed in the magnetosphere.
Abstract: This paper presents an exact analytical model for
optimizing stability of thin-walled, composite, functionally graded
pipes conveying fluid. The critical flow velocity at which divergence
occurs is maximized for a specified total structural mass in order to
ensure the economic feasibility of the attained optimum designs. The
composition of the material of construction is optimized by defining
the spatial distribution of volume fractions of the material
constituents using piecewise variations along the pipe length. The
major aim is to tailor the material distribution in the axial direction so
as to avoid the occurrence of divergence instability without the
penalty of increasing structural mass. Three types of boundary
conditions have been examined; namely, Hinged-Hinged, Clamped-
Hinged and Clamped-Clamped pipelines. The resulting optimization
problem has been formulated as a nonlinear mathematical
programming problem solved by invoking the MatLab optimization
toolbox routines, which implement constrained function
minimization routine named “fmincon" interacting with the
associated eigenvalue problem routines. In fact, the proposed
mathematical models have succeeded in maximizing the critical flow
velocity without mass penalty and producing efficient and economic
designs having enhanced stability characteristics as compared with
the baseline designs.
Abstract: We study dynamic instability in high-rise steel moment
resisting frames (SMRFs) subjected to synthetic long-period ground
motions caused by hypothetical huge subduction earthquakes. Since
long duration as well as long dominant periods is a characteristic of
long-period ground motions, interstory drifts may enter the negative
postyield stiffness range many times when high-rise buildings are
subjected to long-period ground motions. Through the case studies of
9 high-rise SMRFs designed in accordance with the Japanese design
practice in 1980s, we demonstrate that drifting, or accumulation of
interstory drifts in one direction, occurs at the lower stories of the
SMRFs, if their natural periods are close to the dominant periods of the
long-period ground motions. The drifting led to residual interstory
drift ratio over 0.01, or to collapse if the design base shear was small.
Abstract: The purpose of this work is fast design optimization of
the seal chamber. The study includes the mass transfer between lower
and upper chamber on seal chamber for hot water application pumps.
The use of Fluent 12.1 commercial code made it possible to capture
complex flow with heat-mass transfer, radiation, Tailor instability,
and buoyancy effect. Realizable k-epsilon model was used for
turbulence modeling. Radiation heat losses were taken into account.
The temperature distribution at seal region is predicted with respect
to heat addition.
Results show the possibilities of the model simplifications by
excluding the water domain in low chamber from calculations. CFD
simulations permit to improve seal chamber design to meet target
water temperature around the seal. This study can be used for the
analysis of different seal chamber configurations.
Abstract: The motorway segment between Tangier and Oued
R’mel has experienced, since the beginning of building works,
significant instability and landslides linked to a number of geological,
hydrogeological and geothermic factors affecting the different
formations.
The landslides observed are not fully understood, despite many
studies conducted on this segment. This study aims at producing new
methods to better explain the phenomena behind the landslides,
taking into account the geotechnical and geothermic contexts. This
analysis builds up on previous studies and geotechnical data collected
in the field.
The final body of data collected shall be processed through the
Plaxis software for a better and customizable view of the landslide
problems in the area, which will help tofind solutions and stabilize
land in the area.
Abstract: In this work, we incorporated a quartic bond potential
into a coarse-grained bead-spring model to study lubricant adsorption
on a solid surface as well as depletion instability. The surface tension
density and the number density profiles were examined to verify the
solid-liquid and liquid-vapor interfaces during heat treatment. It was
found that both the liquid-vapor interfacial thickness and the
solid-vapor separation increase with the temperatureT* when T*is
below the phase transition temperature Tc
*. At high temperatures
(T*>Tc
*), the solid-vapor separation decreases gradually as the
temperature increases. In addition, we evaluated the lubricant weight
and bond loss profiles at different temperatures. It was observed that
the lubricant desorption is favored over decomposition and is the main
cause of the lubricant failure at the head disk interface in our
simulations.
Abstract: Until recently, energy security and climate change
were considered separate issues to be dealt with by policymakers.
The two issues are now converging, challenging the security and
climate communities to develop a better understanding of how to deal
with both issues simultaneously. Although Egypt is not a major
contributor to the world's total GHG emissions, it is particularly
vulnerable to the potential effects of global climate change such as
rising sea levels and changed patterns of rainfall in the Nile Basin.
Climate change is a major threat to sustainable growth and
development in Egypt, and the achievement of the Millennium
Development Goals. Egypt-s capacity to respond to the challenges of
climate instability will be expanded by improving overall resilience,
integrating climate change goals into sustainable development
strategies, increasing the use of modern energy systems with reduced
carbon intensity, and strengthening international initiatives. This
study seeks to establish a framework for considering the complex and
evolving links between energy security and climate change,
applicable to Egypt.
Abstract: It has been always observed that the effectiveness of
MIS as a support tool for management decisions degenerate after
time of implementation, despite the substantial investments being
made. This is true for organizations at the initial stages of MIS
implementations, manual or computerized. A survey of a sample of
middle to top managers in business and government institutions was
made. A large ratio indicates that the MIS has lost its impact on the
day-to-day operations, and even the response lag time expands
sometimes indefinitely. The data indicates an infant mortality
phenomenon of the bathtub model. Reasons may be monotonous
nature of MIS delivery, irrelevance, irreverence, timeliness, and lack
of adequate detail. All those reasons collaborate to create a degree of
degeneracy. We investigate and model as a bathtub model the
phenomenon of MIS degeneracy that inflicts the MIS systems and
renders it ineffective. A degeneracy index is developed to identify
the status of the MIS system and possible remedies to prevent the
onset of total collapse of the system to the point of being useless.
Abstract: A liquid curved jet has many applications in different
industrial and engineering processes, such as the prilling process
for generating small spherical pellets (fertilizer or magnesium). The
liquids used are usually molten and contain small quantities of
polymers and therefore can be modelled as non-Newtonian liquids. In
this paper, we model the viscoelastic liquid jet by using the Oldroyd-
B model. An asymptotic analysis has been used to simplify the
governing equations. Furthermore, the trajectory and a linear temporal
stability in the presence of gravity and rotation have been determined.
Abstract: A seismic isolation pad produced by utilizing the scrap
tire rubber which contains interleaved steel reinforcing cords has been
proposed. The steel cords are expected to function similar to the steel
plates used in conventional laminated rubber bearings. The scrap tire
rubber pad (STRP) isolator is intended to be used in low rise
residential buildings of highly seismic areas of the developing
countries. Experimental investigation was conducted on unbonded
STRP isolators, and test results provided useful information including
stiffness, damping values and an eventual instability of the isolation
unit. Finite element analysis (FE analysis) of STRP isolator was
carried out on properly bonded samples. These types of isolators
provide positive incremental force resisting capacity up to shear strain
level of 155%. This paper briefly discusses the force deformation
behavior of bonded STRP isolators including stability of the isolation
unit.
Abstract: High performance Resistive Random Access Memory
(RRAM) based on HfOx has been prepared and its temperature
instability has been investigated in this work. With increasing
temperature, it is found that: leakage current at high resistance state
increases, which can be explained by the higher density of traps
inside dielectrics (related to trap-assistant tunneling), leading to a
smaller On/Off ratio; set and reset voltages decrease, which may be
attributed to the higher oxygen ion mobility, in addition to the
reduced potential barrier to create / recover oxygen ions (or oxygen
vacancies); temperature impact on the RRAM retention degradation
is more serious than electrical bias.
Abstract: Transient Stability is an important issue in power systems planning, operation and extension. The objective of transient stability analysis problem is not satisfied with mere transient instability detection or evaluation and it is most important to complement it by defining fast and efficient control measures in order to ensure system security. This paper presents a new Fuzzy Support Vector Machines (FSVM) to investigate the stability status of power systems and a modified generation rescheduling scheme to bring back the identified unstable cases to a more economical and stable operating point. FSVM improves the traditional SVM (Support Vector Machines) by adding fuzzy membership to each training sample to indicate the degree of membership of this sample to different classes. The preventive control based on economic generator rescheduling avoids the instability of the power systems with minimum change in operating cost under disturbed conditions. Numerical results on the New England 39 bus test system show the effectiveness of the proposed method.
Abstract: In many buildings we rely on large footings to offer
structural stability. Designers often compensate for the lack of
knowledge available with regard to foundation-soil interaction by
furnishing structures with overly large footings. This may lead to a
significant increase in building expenditures if many large
foundations are present. This paper describes the interface material
law that governs the behavior along the contact surface of adjacent
materials, and the behavior of a large foundation under ultimate limit
loading. A case study is chosen that represents a common
foundation-soil system frequently used in general practice and
therefore relevant to other structures. Investigations include
compressing versus uplifting wind forces, alterations to the
foundation size and subgrade compositions, the role of the slab
stiffness and presence and the effect of commonly used structural
joints and connections. These investigations aim to provide the
reader with an objective design approach, efficiently preventing
structural instability.
Abstract: The approach of subset selection in polynomial
regression model building assumes that the chosen fixed full set of
predefined basis functions contains a subset that is sufficient to
describe the target relation sufficiently well. However, in most cases
the necessary set of basis functions is not known and needs to be
guessed – a potentially non-trivial (and long) trial and error process.
In our research we consider a potentially more efficient approach –
Adaptive Basis Function Construction (ABFC). It lets the model
building method itself construct the basis functions necessary for
creating a model of arbitrary complexity with adequate predictive
performance. However, there are two issues that to some extent
plague the methods of both the subset selection and the ABFC,
especially when working with relatively small data samples: the
selection bias and the selection instability. We try to correct these
issues by model post-evaluation using Cross-Validation and model
ensembling. To evaluate the proposed method, we empirically
compare it to ABFC methods without ensembling, to a widely used
method of subset selection, as well as to some other well-known
regression modeling methods, using publicly available data sets.
Abstract: Pakistani doctors (MBBS) are emigrating towards developed countries for professional adjustments. This study aims to highlight causes and consequences of doctors- brain drain from Pakistan. Primary data was collected from Mayo Hospital, Lahore by interviewing doctors (n=100) through systematic random sampling technique. It found that various socio-economic and political conditions are working as push and pull factors for brain drain of doctors in Pakistan. Majority of doctors (83%) declared poor remunerations and professional infrastructure of health department as push factor of doctors- brain drain. 81% claimed that continuous instability in political situation and threats of terrorism are responsible for emigration of doctors. 84% respondents considered fewer opportunities of further studies responsible for their emigration. Brain drain of doctors is affecting health sector-s policies / programs, standard doctor-patient ratios and quality of health services badly.