30,434 research outputs found
The hydraulic bump: The surface signature of a plunging jet
When a falling jet of fluid strikes a horizontal fluid layer, a hydraulic
jump arises downstream of the point of impact provided a critical flow rate is
exceeded. We here examine a phenomenon that arises below this jump threshold, a
circular deflection of relatively small amplitude on the free surface, that we
call the hydraulic bump. The form of the circular bump can be simply understood
in terms of the underlying vortex structure and its height simply deduced with
Bernoulli arguments. As the incoming flux increases, a breaking of axial
symmetry leads to polygonal hydraulic bumps. The relation between this
polygonal instability and that arising in the hydraulic jump is discussed. The
coexistence of hydraulic jumps and bumps can give rise to striking nested
structures with polygonal jumps bound within polygonal bumps. The absence of a
pronounced surface signature on the hydraulic bump indicates the dominant
influence of the subsurface vorticity on its instability
Calculation of Elastic Green's Functions for Lattices with Cavities
In this Brief Report, we present an algorithm for calculating the elastic
Lattice Greens Function of a regular lattice, in which defects are created by
removing lattice points. The method is computationally efficient, since the
required matrix operations are on matrices that scale with the size of the
defect subspace, and not with the size of the full lattice. This method allows
the treatment of force fields with multi-atom interactions.Comment: 3 pages. RevTeX, using epsfig.sty. One figur
Distributional Impacts of CAP Adoption on Romanian Households
This paper focuses on estimation of distributional economic welfare effects of the adoption of the CAP on different groups of Romanian households. The calculations of welfare effects are based on 1999 household data and refer to a 10-fold breakdown of Romanian households, i.e. five socio-economic categories from urban and rural areas, taking into account own (home) production of food. To identify the most vulnerable groups of Romanian consumers to food price changes, the Slutsky approximation Compensating Variation approach is applied. The results suggest that, if the current CAP is adopted and results in food price changes averaging a 10 per cent increase in all food prices, the lowest-income groups (i.e. urban and rural unemployed households, urban pensioner households) will be the most affected, ceteris paribus (prices of all other goods held constant). The minimum amount by which the groups could be compensated for the effect of price change on their real incomes varies between Euro 3 per month for employers' households (about 1% of total income) and about Euro 8 per month for farmers' households (6%). However, due to the relatively large shares of food self-production in total consumption, in particular by rural households, somewhat smaller money compensation would be appropriate.distributional economic effects, CAP, Slutsky approximation, Compensating Variation, Romania, Agricultural and Food Policy,
Performance of Particle Flow Calorimetry at CLIC
The particle flow approach to calorimetry can provide unprecedented jet
energy resolution at a future high energy collider, such as the International
Linear Collider (ILC). However, the use of particle flow calorimetry at the
proposed multi-TeV Compact Linear Collider (CLIC) poses a number of significant
new challenges. At higher jet energies, detector occupancies increase, and it
becomes increasingly difficult to resolve energy deposits from individual
particles. The experimental conditions at CLIC are also significantly more
challenging than those at previous electron-positron colliders, with increased
levels of beam-induced backgrounds combined with a bunch spacing of only 0.5
ns. This paper describes the modifications made to the PandoraPFA particle flow
algorithm to improve the jet energy reconstruction for jet energies above 250
GeV. It then introduces a combination of timing and p_T cuts that can be
applied to reconstructed particles in order to significantly reduce the
background. A systematic study is performed to understand the dependence of the
jet energy resolution on the jet energy and angle, and the physics performance
is assessed via a study of the energy and mass resolution of W and Z particles
in the presence of background at CLIC. Finally, the missing transverse momentum
resolution is presented, and the fake missing momentum is quantified. The
results presented in this paper demonstrate that high granularity particle flow
calorimetry leads to a robust and high resolution reconstruction of jet
energies and di-jet masses at CLIC.Comment: 14 pages, 11 figure
Sensitivity-analysis method for inverse simulation application
An important criticism of traditional methods of inverse simulation that are based on the Newton–Raphson algorithm is that they suffer from numerical problems. In this paper these problems are discussed and a new method based on sensitivity-analysis theory is developed and evaluated. The Jacobian matrix may be calculated by solving a sensitivity equation and this has advantages over the approximation methods that are usually applied when the derivatives of output variables with respect to inputs cannot be found analytically. The methodology also overcomes problems of input-output redundancy that arise in the traditional approaches to inverse simulation. The sensitivity- analysis approach makes full use of information within the time interval over which key quantities are compared, such as the difference between calculated values and the given ideal maneuver after each integration step. Applications to nonlinear HS125 aircraft and Lynx helicopter models show that, for this sensitivity-analysis method, more stable and accurate results are obtained than from use of the traditional Newton–Raphson approach
A simple derivation of the electromagnetic field of an arbitrarily moving charge
The expression for the electromagnetic field of a charge moving along an
arbitrary trajectory is obtained in a direct, elegant, and Lorentz invariant
manner without resorting to more complicated procedures such as differentiation
of the Lienard-Wiechert potentials. The derivation uses arguments based on
Lorentz invariance and a physically transparent expression originally due to
J.J.Thomson for the field of a charge that experiences an impulsive
acceleration.Comment: The following article has been accepted by the American Journal of
Physics. After it is published, it will be found at
http://scitation.aip.org/ajp; 12 pages, 1 figur
- …