bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure, composition, and diversity of old-growth black spruce boreal forest of the Clay Belt region in Quebec and Ontario
Authors: Harper Karen , Boudreault Catherine , DeGrandpré Louis , Drapeau Pierre , Gauthier Sylvie , Bergeron Yves
Published: September 2003

Old-growth black spruce (Picea mariana) boreal forest in the Clay Belt region of Ontario and Quebec is an open forest with a low canopy, quite different from what many consider to be "old growth". Here, we provide an overview of the characteristics of old-growth black spruce forest for three different site types on organic, clay, and coarse deposits. Our objectives were (1) to identify the extent of older forests; (2) to describe the structure, composition, and diversity in different age classes; and (3) to identify key processes in old-growth black spruce forest. We sampled canopy composition, deadwood abundance, understorey composition, and nonvascular plant species in 91 forest stands along a chronosequence that extended from 20 to more than 250 years after fire. We used a peak in tree basal area, which occurred at 100 years on clay and coarse sites and at 200 years on organic sites, as a process-based means of defining the start of old-growth forest. Old-growth forests are extensive in the Clay Belt, covering 3050% of the forested landscape. Black spruce was dominant on all organic sites, and in all older stands. Although there were fewer understorey species and none exclusive to old-growth, these forests were structurally diverse and had greater abundance of Sphagnum, epiphytic lichens, and ericaceous species. Paludification, a process characteristic of old-growth forest stands on clay deposits in this region, causes decreases in tree and deadwood abundance. Old-growth black spruce forests, therefore, lack the large trees and snags that are characteristic of other old-growth forests. Small-scale disturbances such as spruce budworm and windthrow are common, creating numerous gaps. Landscape and stand level management strategies could minimize structural changes caused by harvesting, but unmanaged forest in all stages of development must be preserved in order to conserve all the attributes of old-growth black spruce forest. Key words: boreal forest, old growth, paludification, Picea mariana, structural development, succession.
Patterns of bryophyte diversity in humid coastal and inland cedarhemlock forests of British Columbia
Authors: Newmaster Steven G , Belland René J , Arsenault André , Vitt Dale H
Published: September 2003

Mosses and hepatics (bryophytes) are the most diverse and abundant understorey vegetation within the Coastal Western Hemlock (CWH) and Interior CedarHemlock (ICH) zones of British Columbia. This study intensively sampled bryophytes in 287 young- and old-growth stands in the CWH and ICH zones. Two major variables strongly influence the patterning of bryophyte diversity in these zones: stand age and habitat heterogeneity. Canonical correspondence analyses (CCA) identified these as the most important variables explaining standenvironment interactions. Alpha diversity is much greater in old-growth forests and beta diversity is high between young and old forests. Old-growth cedarhemlock forests have between 60 (ICH) and 100% (CWH) more species than younger forests disturbed by wildfire in the ICH zones or logging in the CWH zones. Furthermore, a stand classification built on species composition partitioned species into stands of different ages and mesohabitat heterogeneity. Beta diversity was also partitioned between stands of different ages and habitat heterogeneity. This indicates that both young and old forests have a unique assemblage of species. Indicator analysis was used to choose a partial lists of species that are indicators of "old growthness". These old forests support a rich flora of hepatics and rare western North American endemics. High environmental continuity is associated with the most humid watersheds and cedarhemlock forests within these watersheds have the highest bryophyte diversity. The establishment of rich communities of bryophytes in the moist cedarhemlock forest has been occurring over the last 20007000 years, with the coastal rainforest much older than the inland rainforest. Large-scale disturbance, such as forestry, threatens the existence of these highly diverse communities. A better understanding of the patterning of bryophyte diversity will provide an opportunity to minimize the impact of forest operations on biodiversity. Bryophyte diversity in British Columbia cedarhemlock forests will be sustained through ecosystem management of old-growth legacies (i.e., landscapes, stands, and their components) and preservation of areas of high diversity. Temporal and habitat variables are influential in the patterning of bryophyte diversity. Management plans that consider these variables will be better equipped to manage cedarhemlock forests for maintaining biodiversity. Key words: biodiversity, bryophytes, cedarhemlock, CWH, disturbance, ecosystem management, floristic habitat sampling, forest conservation, ICH, old growth, patterning of diversity, rare species, species richness.
Overview of old-growth forests in Canada from a science perspective
Authors: Mosseler A , Thompson I , Pendrel B A
Published: September 2003

In response to a broad public concern about the rapidly diminishing area of old-growth forests and their intrinsic biological value, the Canadian Forest Service organized a national symposium in 2001 to discuss the old-growth issue from a science perspective. The objectives were: (i) to bring together Canadian expertise on old-growth forests, (ii) to define old growth within the main forest regions of Canada, (iii) to understand its biological complexities and ecological roles, and (iv) to discuss management and restoration experiences and options. Some forest regions of Canada still contain significant old-growth forest (e.g., some boreal forest regions), although other regions contain very little primary, relatively undisturbed, older forest (e.g., eastern temperate-zone forest regions). One of the difficulties in managing and conserving old-growth forests is defining them in a scientifically meaningful, yet operational and policy-relevant manner. This difficulty may be overcome by developing an index of "old-growthness" (Spies and Franklin 1988) related to specific forest regions or forest types. Such an old-growth index would allow for the inclusion of specific attributes, composition, functions, and processes seen as relevant to different ecological regions or specific forest types and could serve as a basis for prioritizing local or regional conservation and management activities. Thus, such an index approach has worldwide applicability. Traditionally, old-growth forests have been valued primarily as habitat for forest-dependent, specifically old-growth-dependent, wildlife. Recent results from research on old-growth forests in eastern Canada suggest that as tree populations age they tend to increase in genetic diversity and reproductive fitness, suggesting that old-growth forests may serve as natural reservoirs of genetic diversity and reproductive fitness for the constituent tree species. This has important implications for the dispersal and adaptation of trees across increasingly fragmented forest landscapes subject to the anticipated rapid climatic changes and the introduction of new pest and disease problems. Old-growth conservation goes well beyond the more traditional areas of watershed (including water quality) and habitat protection and includes emerging issues such as the conservation of genetic resources and carbon sequestration. It is very much a cross-sectoral issue with many interdisciplinary linkages. Therefore, conservation and protection of old-growth forests should be of wide general interest to the forest sector. Key words: biodiversity conservation, Canada's forests, genetic diversity, late-successional temperate forests, old-growth index, reproductive fitness.
L (X-ray) cross sections of heavy elements excited by 15.20 keV photons
Authors: Saad M
Published: September 2003

In this work Lα and Lβ X-ray fluorescence cross sections and their relative intensities ILβ  / ILα were measured for the elements La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu using a photon energy of 15.20 keV. Reasonable agreement is obtained between the present experimental results and the theoretically calculated values of L X-ray cross sections and their relative intensities.

PACS Nos.: 32.30.Rj, 32.50.td
Heat transfer over a stretching surface with internal heat generation
Authors: Elbashbeshy E MA , Bazid M AA
Published: September 2003

Heat transfer over a stretching surface with internal heat generation or absorption is examined. The surface is moving with a power-law velocity distribution. The effect of various governing parameters, such as the Prandtl number, the velocity exponent, and the heat-source/sink parameter on the velocity profiles, temperature profiles, and rate of heat transfer are analyzed.

PACS No.: 44.20.tb
Natural-frequency concept utilized in remote probing of the earth
Authors: Bishay S T , Abo-Seida O M , Sami G M
Published: September 2003

The complete time-domain fields due to a vertical magnetic dipole on the surface of a two-layered earth model are derived in an analytical form using the natural-frequency concept. In these expressions, the displacement currents in the earth's layers are taken into consideration. The step responses of the induced voltage in a horizontal receiving loop is found to have definite diagnostic features for the ground beneath. These features are demonstrated by numerical results and shown by figures. The clear distinction between the step response of the homogeneous and the two-layered ground suggests that this response can be used for the detection of the stratification.

PACS Nos.: 41.20.Jb, 42.25.Bs, 42.25.Gy, 44.05.+e
Level energies and oscillator strengths in Ni(XII)
Authors: Singh Narendra , Singh Avnindra K , Mohan Man
Published: September 2003

Configuration interaction wave functions have been calculated and used to evaluate oscillator strengths and transition probabilities for dipole-allowed transitions from the ground-state levels to those of the 3s3p6 and 3s23p43d states of Ni(XII), in both LS and LSJ coupling schemes. Lifetimes of the excited levels are determined. The present results are compared with other available calculations and experiments. PACS No.: 32.70.Cs
Dynamical quantization and classical limit
Authors: Bolivar A O
Published: September 2003

We have worked out a quantization method directly from classical dynamics without using Hamiltonian and Lagrangian functions; we call it dynamical quantization. The present article compares such a method with the Dirac and Feynman quantization procedures and also verifies the logical consistence of the dynamical quantization calculating the classical limit of a Brownian particle, for example.

PACS Nos.: 03.65.w, 05.30.d, 05.40.+j, 52.65.Ff
Transient fields of a vertical electric dipole on an M-layered dielectric medium
Authors: Abo-Seida O M , Sami G M
Published: September 2003

A simple and explicit derivation for the vertical electric dipole excited by a short-pulse current and located above a layered dielectric medium is derived in an analytical form using the Cagniardde Hoop method. The fields are expressed as the convolution of the exciting current with the layered medium response. This response is obtained directly from the integral representation for the magnetic fields in the frequency domain and is expressed as a finite integral. A modified Cagniard method is then used to derive closed-form expressions for the vertical dipole anywhere above a multilayered medium. The method is used to perform numerical calculations of the magnetic fields for applications to geo-radar operating on layered media. PACS Nos.: 41.20.Jb, 42.25.Bs, 42.25.Gy
Apport de la collimation assistée par ordinateur à l'amélioration de la qualité de l'image en tomographie d'émission monophotonique
Authors: Elloumi I
Published: September 2003

Computer-assisted collimation (CAC) is a new project to improve both resolution and sensitivity in single photon emission computed tomography. The image reconstruction takes full account of the variation of the response with regards to the distance between the source and the detector. The global signal-to-noise ratio of the image in CAC is noticeably improved. The resolution and local signal-to-noise ratio are homogeneous and depend little on the object depth. The uncertainty over the volume of the object irradiating the element detector and the uncertainty over the number of counts in this element are reduced.
Electromagnetic scattering by a lossy dielectric-coated elliptic cylinder
Authors: Hamid A -K , Hussein M I
Published: September 2003

The problem of electromagnetic wave scattering by a lossy dielectric-coated elliptic cylinder is analyzed using elliptic waves expressed in terms of complex Mathieu functions. Numerical results are obtained for the scattered field in the far zone for different axial ratios, lossy dielectric constants, and angles of incidence. The numerical results show a significant change in backscattering echo due to the lossy dielectric coating.

PACS No.: 42.25.Fx
The effect of an axial electric field on the nonlinear stability between two uniform stream flows of finitely conducting cylinders
Authors: Elhefnawy Abdel Raouf F , Moatimid Galal M , Khalil Elcoot Abd Elmonem
Published: September 2003

Weakly nonlinear streaming instability of two conducting fluids with an interface is presented for cylinders of circular cross section. The two fluids are subjected to a uniform axial electric field. Gravitational effects are neglected. The method of multiple scale perturbation is used to obtain a dispersion relation for the first-order problem and two nonlinear Schrödinger equations for the higher orders. The nonlinear Schrödinger equation, generally, describes the competition between nonlinearity and a linear dispersion relation. One of these equations is used to determine the nonlinear cutoff electric field separating stable and unstable disturbances, while the other is used to analyze the stability of the system. The stability criterion is expressed theoretically in terms of various parameters of the problem. Stability diagrams are obtained for different sets of physical parameters. New instability regions in the parameter space, which appear due to nonlinear effects, are indicated.

PACS Nos.: 47.20, 47.55.C, 47.65
Forced gravity waves in two-layered fluids with the upper fluid having a free surface
Authors: Sherief H H , Faltas M S , Saad E I
Published: September 2003

The steady-gravity wave motion is considered for two immiscible layers of incompressible and nonviscous fluids in the presence of a porous wave maker immersed vertically in the two fluids, the upper fluid having a free surface and the lower fluid is of infinite depth. The boundary value problem for the velocity potentials is solved using Taylor's assumption on the wave maker. Also the scattering of a harmonic wave incident normally to the wave maker is considered and the reflection and transmission coefficients are obtained. The case when the lower fluid is of finite depth is also considered. The results are plotted for different values of porosity and different values of the density ratio.

PACS Nos.: 47.35.+i, 47.55.Hd, 47.55.Mh
The effect of thermal relaxation time on a electrohydrodynamic viscoelastic fluid layer heated from below
Authors: Othman M IA , Zaki S A
Published: September 2003

The problem of the onset of stability in a horizontal layer of a viscoelastic dielectric liquid with one relaxation time heated from below under the action of a vertical ac electric field is analyzed. Linear stability theory is used to derive an eigenvalue system of order eight and an exact eigenvalue equation for a neutral instability is obtained. Under somewhat artificial boundary conditions, this equation can be solved exactly to yield the required eigenvalue relationship from which various critical values are determined in detail. The critical Rayleigh number and wave number for the onset of instability are presented graphically as functions of the Grashof number for various values of the Prandtl number and one relaxation time. A comparison is made with the results obtained in the absence of an electric field.

PACS No.: 47.27.T
A high-speed-modulated retro-reflector for lasers using an acousto-optic modulator
Authors: Spirou G , Yavin I , Weel M , Vorozcovs A , Kumarakrishnan A , Battle P R , Swanson R C
Published: September 2003

We have used an acousto-optic modulator (AOM) to impose a frequency-modulated signal on an incident laser beam. The incident laser beam is focussed into the AOM where it undergoes Bragg diffraction and is then retro-reflected. The diffracted beam is also retro-reflected so that it is diffracted again by the AOM and overlaps the incident beam. The overlapped beams are frequency shifted with respect to each other. These features allow us to detect the frequency-modulated signal with high signal-to-noise ratio using heterodyne detection. Since the optical setup is simple and can be made very compact, this device may be ideal for certain forms of high-speed, free-space optical communication. We demonstrate a 1 MHz data transmission rate in the Bragg regime. We measured the acceptance angle of the device and find that it is limited only by the divergence of the focussed laser beam and the divergence of the acoustic waves in the AOM crystal. We have also studied the range of acoustic frequencies and drive power of the AOM, for which the retro-reflected beam can be detected with adequate signal to noise.

PACS Nos.: 42.60.V, 42.62.Cf, 42.62.Fi, 42.79.Sz, 42.79.Hp
Near-threshold ionization of atoms and molecules by positron impact
Authors: Campeanu R I , Nagy L , Stauffer A D
Published: September 2003

Distorted-wave models previously used to study the ionization of hydrogen and the noble gases by positron impact at medium kinetic energies are employed to produce cross sections for impact energies within 0.02 eV of the ionization threshold. These theoretical cross sections are compared with the WannierKlar threshold power-law formula and the existing experimental results. PACS Nos.: 34.50.Fa, 34.85.+x
Calculation of the transfer efficiency between dual magneto-optical traps and simulation of a Ioffe trap for BoseEinstein condensation
Authors: Yavin I , Mikaelian T , Kumarakrishnan A
Published: September 2003

We consider the problem of transferring a cold atomic cloud from a low-vacuum chamber to an ultra-high-vacuum (UHV) chamber, where it can be recaptured and cooled to the transition temperature for BoseEinstein condensation (BEC). Our calculation assumes an initial MaxwellBoltzmann velocity distribution for the thermal cloud and a Gaussian spatial density distribution that is characteristic of magneto-optical traps (MOTs). Using a coordinate transformation we find the density of the recaptured atomic cloud as a function of time. This allows us to investigate the effect of experimental parameters on the transfer efficiency. These parameters include the distance of separation between the two chambers, the duration of the initial on-resonant laser used to push the thermal cloud, and the initial cloud temperature. We also present numerical simulations of the magnetic field due to a simplified IoffePritchard (IP) trap that has recently been used to obtain BEC using laser-cooling techniques. This trap converts a quadrupole magnetic field into an IP configuration using the magnetic field of a conical solenoid placed orthogonally to the axis of symmetry of a pair of quadrupole coils. Our results are suitable for small experimental groups interested in achieving BEC.

PACS No.: 03.75
A high-speed retro-reflector for free-space communication based on electro-optic phase modulation
Authors: Mikaelian T , Weel M , Kumarakrishnan A , Battle P R , Swanson R C
Published: September 2003

We demonstrate that an electro-optic phase modulator (EOM) can be used as a constituent of a corner-cube-based modulated high-speed retro-reflector. We performed experiments to investigate the efficiency of the phase modulation produced by an EOM as a function of the angle of a laser beam incident on it. Our experiments demonstrate that the field of view of the EOM is determined by its dimensions and the diameter of the laser beam. This suggests that the device may be suitable for applications involving high-speed (GHz), free-space communication. In these applications, the retro-reflector can be mounted on a moving platform such as a satellite. We find that it is possible to detect the retro-reflected signal with an adequate signal-to-noise ratio using heterodyne detection. We also discuss some practical considerations necessary for the implementation of such a device.

PACS Nos.: 42.60.V, 42.62.Cf, 42.62.Fi, 42.79.Sz, 42.79.Hp
Identification of semiclassical chaos in two-dimensional PT-symmetric systems
Authors: Nanayakkara Asiri , Abayaratne Chula
Published: September 2003

Identification of regular and chaotic motions of two-dimensional PT-symmetric complex systems was investigated. New definitions have been introduced to study properties of trajectories in complex phase space. Projections of these trajectories on complex x- and y-planes, Lyapunov exponents, and surfaces of section have been used for identifying regular and irregular (chaotic) motions in complex phase space. Quantum level spacing distributions of these systems have also been calculated for finding out the connection between regular and irregular states with standard distributions such as Poisson and Wigner distributions. It has been found that the PT-symmetric complex systems behave in the same way as the real systems.

PACS No.: 05.45.Ac
Unsteady flow of a dusty conducting non-Newtonian fluid through a pipe
Authors: Attia H A
Published: September 2003

In this paper, the unsteady flow of a dusty viscous incompressible electrically conducting non-Newtonian power-law fluid through a circular pipe is investigated. A constant pressure gradient in the axial direction and a uniform magnetic field directed perpendicular to the flow direction are applied. The particle phase is assumed to behave as a viscous fluid. A numerical solution is obtained for the governing nonlinear momentum equations using finite differences. The effects of the magnetic-field parameter Ha, the non-Newtonian fluid characteristics (the flow index n), and the particle-phase viscosity β on the transient behavior of the velocity, volumetric flow rates, and skin friction coefficients of both fluid and particle phases are studied. It is found that all the flow parameters for both phases decrease as the magnetic field increases or the flow index decreases. On the other hand, increasing the particle-phase viscosity increases the skin friction of the particle phase, but decreases the other flow parameters.

PACS No.: 47.50.+d
Comment on "A simple explanation of the nonappearance of physical gluons and quarks"
Authors: Aste Andreas
Published: September 2003

In a recent paper by Johan Hansson it is claimed that the nonappearance of quarks and gluons as physical particles is an automatic result of the non-Abelian nature of the color interaction in quantum chromodynamics. It is shown that the arguments given by Hansson are insufficient to support his claim by giving simple counter arguments.

PACS No.: 11.10.z
Analytical formulas for the Stark effect on intensity of hydrogen radiation lines
Authors: Kamenski A A , Ovsiannikov V D
Published: September 2003

A regular method for deriving the consecutive terms of a series in powers of field strength F for the intensities of hydrogen radiation lines is presented both analytically and numerically. Specific modification of the perturbation theory for degenerate states and the Sturm-series expansion for the completely reduced CoulombGreen function in parabolic coordinates are used to derive simple analytical formulas for matrix elements and the intensities of the radiation transitions between circular states. Particular cases of transitions between the closest Rydberg levels are presented and discussed in detail. Analytical expressions are also derived for the quadrupole matrix elements, which may contribute to the probability of σ-transitions with the selection rule for the magnetic quantum number Δm = ±1 and determine the probability of the dipole-forbidden radiation transitions between Stark levels with Δm = ±2.

PACS Nos.: 32.60.+i, 32.70.n, 32.70.Fw
Investigation of the elastic properties of UNI2Si2 as a function of temperature, magnetic field, and pressure
Authors: Quirion G , Kelly A , Newbury S , Razavi F S , Garrett J D
Published: September 2003

It is now well-established that the strong anisotropy in the magnetic properties of the intermetallic compounds UT2Si2, where T stands for a transition metal, is responsible for their rich magnetic phase diagram. However, within that series of compounds, UNi2Si2 is one that shows an unusual sequence of magnetically ordered states. Thus, to better understand its unusual properties, we have investigated the elastic properties of UNi2Si2 as a function of temperature, magnetic field, and pressure. In all three magnetic phases, our measurements indicate that the sound-velocity temperature dependence is dominated by the magnetoelastic coupling. Moreover, the analysis of the temperature dependence for the incommensurate longitudinal spin-density wave phase is consistent with a critical exponent β = 0.38 ± 0.01. We also present the magnetic phase diagram for UNi2Si2 obtained at 0 and 8 kbar. Our investigation reveals that the triple-point coordinates (Tp, Hp) decrease with pressure at a rate of dTp/dP = 0.1 K/kbar and dHp/dP = 0.1 T/kbar, respectively.

PACS Nos.: 75.30.kz, 62.20.Dc, 62.50.+p, 75.40.Cx
Strain field due to transition-metal impurities in Fe
Authors: Sharma H , Prakash S
Published: September 2003

The Kanzaki lattice static method is used to calculate the strain field due to substitutional transition-metal impurities in Fe. The effective ionion interaction potential due to Wills and Harrison is used to calculate the dynamical matrix and the impurity-induced force up to second nearest neighbor of impurity. The atomic displacements due to 3d, 4d, and 5d substitutional transition-metal impurities (Cr, Mn, Ni, Cu, Nb, Mo, W, and Pt ) are calculated up to 24 nearest neighbors. The displacements are minimum for 3d impurities Cr and Mn and maximum for 4d impurity Nb. A similar trend is found in the calculated relaxation energy also. The calculated values are in qualitative agreement with the available experimental data.
Modeling wind and altitude effects in the 200 m sprint
Authors: Mureika J R
Published: September 2003

A quasi-realistic mathematical model of 100 m sprint performances is modified to simulate the 200 m race, a portion of which is run around a curve. The calculated effects of wind are complex functions of the wind direction and the lane in which the athlete is running. It is shown that wind and altitude-assisted marks for the 200 m are in some cases significantly higher than the corresponding adjustments for the 100 m sprint under similar conditions. The estimated advantage of a 2 m s1 tail wind is between 0.090.14 s, with the greater advantage going to the runner in the outside lane. At higher altitudes (>2000 m), these corrections can rise to over 0.3 s. Crosswinds can further enhance the performance by over 0.5 s due to decreased drag forces around the curve. A consequence of these results suggests that record ratification procedures for such performances be reconsidered. The model is also used to study Michael Johnson's world record race of 19.32 s from the 1996 Olympic Games in Atlanta, Georgia. PACS No.: 01.80.L
The Bohm quantum potential and the classical limit of quantum mechanics
Authors: Bolivar A O
Published: September 2003

Using a procedure based on the limit [Formula: see text], we show that the classical limiting method based on the Bohm quantum potential (Q [Formula: see text] 0) is not necessary to characterize the classical limit of quantum mechanics. PACS No.: 03.65.Ta
Reply to the comment by M. Denny on "The motion of a curling rock"
Authors: Shegelski Mark RA , Niebergall Ross
Published: September 2003

We present experimental results for purely rotating curling rocks and show that these results are easily accounted for by "wet" friction and cannot be explained in terms of "dry" friction. We also list other observed motions of curling rocks that can be understood in terms of wet friction and not dry friction.

PACS Nos.: 01.80.+b, 45.40.f
Classical orbits from the wave function in the large-quantum-number limit
Authors: Bonnar James D , Schmidt Jeffrey R
Published: September 2003

Classical trajectories for the Coulomb potential are obtained from the large principle quantum-number limit of solutions to the nonrelativistic Schrödinger equation, by use of integral equations satisfied by the radial probability density function. These trajectories are found to be in excellent agreement with those computed directly from classical mechanics, in accordance with a statement of the Bohr Correspondence principle, except in a region very close to the center of force. PACS No.: 05.45.Mt
Comment on "The motion of a curling rock"
Authors: Denny Mark
Published: September 2003

We investigate the model adopted in a recent paper in which the authors seek to explain the observed trajectory of a curling rock. We question the basis upon which the model is built, namely, frictional asymmetry arising from kinematic melting of the ice, and establish that the forms assumed for fluid friction motion are incorrect. Analytical and experimental results show that the force acting upon curling rocks is dominated by dry friction.

PACS Nos.: 01.80.+b, 45.40.f
On uniqueness and reciprocity theorems for generalized thermo-viscoelasticity with thermal relaxation
Authors: Ezzat Magdy A , El-Karamany Ahmed S
Published: September 2003

The equations of generalized thermo-viscoelasticity for an isotropic medium are given. Using Laplace transforms, a uniqueness theorem for these equations is proved. Also, a reciprocity theorem is obtained and some applications are given.

PACS No.: 46.35.+z
Accurate wavelengths of resonance lines in Zn-like heavy ions
Authors: Utter S B , Beiersdorfer P , Träbert E
Published: September 2003

Using an electron-beam ion trap and a flat-field spectrometer, the extreme ultraviolet resonance lines of Zn-like ions of Yb, W, Au, Pb, Th, and U were observed and their wavelengths measured with greatly improved accuracy. The results are compared to those from laser-produced plasmas and to theory, and significant differences are found. PACS Nos.: 32.30.Jc, 39.30.+w
Reply to the comment by A. Aste on "A simple explanation of the nonappearance of physical gluons and quarks"
Authors: Hansson Johan
Published: September 2003

This is the reply to a comment by Andreas Aste on a previous article of mine in the Canadian Journal of Physics The counter-arguments used by Aste utilize a mathematical limit without physical meaning. We still contend that in QCD, the particles "gluons" and "quarks" are merely artifacts of an approximation method (the perturbative expansion) and are simply absent in the exact theory.

PACS Nos.: 12.38.Aw, 03.70.+k, 11.15.q
Heavy-ion storage-ring quest for atomic lifetimes in Li+ and Be2+
Authors: Träbert E , Gwinner G , Knystautas E J , Wolf A
Published: September 2003

Decays of metastable levels in the He-like ions Li+ and Be2+ were studied at a heavy-ion storage ring. The lifetimes involved span five orders of magnitude (from 0.5 ms to 50 s) and thus test the performance envelope of the experimental technique. For the 1s2s3S1 level in Be2+ ions, our lifetime result of (1.80 ± 0.05) s agrees with accurate nonrelativistic and relativistic calculations. While theory in these cases is expected to be well developed, experience reflects on the capabilities of the experimental arrangement. The time-resolved observations reveal information on cross sections for collisional de-excitation. PACS Nos.: 32.70.Cs, 39.90.+d, 31.50.+w
Exact solutions of the equation for composite scalar particles in quantized electromagnetic waves
Authors: Kruglov S I
Published: September 2003

An equation is considered for a composite scalar particle with polarizabilities in an external quantized electromagnetic plane wave. This equation is reduced to a system of equations for an infinite number of interacting oscillators. After diagonalization, we come to equations for free oscillators. As a result, exact solutions of the equation for a particle are found in a plane-quantized electromagnetic wave of arbitrary polarization. As a particular case, the solution for monochromatic electromagnetic waves is considered. The relativistic coherent states of a particle are constructed using the Poisson distribution of photon numbers. In the limit, when the average photon number [Formula: see text] and the volume V of the quantization tend to infinity (but the photon density [Formula: see text] /V remains constant), the wave function converts to the solution corresponding to the external classical electromagnetic wave. PACS Nos.: 14.40.Aq, 13.40.Ks, 13.40.-f
Unification of Newton's laws of motion
Authors: Antippa A F
Published: September 2003

Newton's three laws of motion are unified into one law (a slightly modified second law), valid in generalized inertial frames (defined by a slightly modified first law), invariant under mass scaling (guaranteed by the third law), and having important implications for the concept of force and the problem of self-energy.

PACS Nos.: 45.20.Dd, 45.50.Jf, 45.05.+x
Aboveground growth responses of understory Abies lasiocarpa saplings to different release cuts
Authors: Krasowski Marek J , Wang Jian R
Published: September 2003

A white birch (Betula papyrifera Marsh.) overstory of a 30+ year old stand was thinned or completely removed, releasing an advance regeneration of subalpine fir (Abies lasiocarpa (Hook.) Nutt.). The overstory was clear-cut (T0), thinned to 600 (T600) or to 1200 (T1200) stems/ha, or left uncut (control). Three years after release, understory responses were best demonstrated by decreasing specific leaf area with increasing release level and by changes to height and radial growth increments. Clear-cutting the overstory stalled the height growth in fir for two seasons and radial growth at the tree base for one season. Compared with the control, the 3-year height increment was proportionally greatest in intermediate trees of T600, and this treatment produced the overall best response in height growth. Complete birch removal produced the best radial growth response despite the initial growth check. However, no release treatment significantly affected the whole tree variables (aboveground biomass, height, diameter at breast height (DBH), live crown ratio) within the studied time frame. Shoot silhouette ratios were lowest in the completely released understory trees, while they were similar to those of the controls in all partial-release treatments. Tree sturdiness (height/DBH ratio) was 8090 in most treatments except T0, where it declined to below 80. Despite this improvement, large trees in T0 have been damaged by wind and snow.
Effects of mechanical stimulus, shade, and nitrogen fertilization on morphology and bending resistance in Douglas-fir seedlings
Authors: Mitchell Stephen J
Published: September 2003

Three-year-old coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were planted in a factorial experiment with three levels of shading (0, 30, and 60%), three levels of mechanical stimulus (staked, freestanding, and bent), and two levels of nitrogen fertilization (0 and 200 kg/ha) to investigate the separate and combined effects of these factors on morphology and bending resistance. Fertilization increased branch angle and increased the sensitivity of branch and leader extension to bending stresses but did not affect volume increment, stem form, or bending resistance. The effects of shading and mechanical treatments on morphology were independent and additive. Shading reduced stem diameter and volume increment, but did not affect height increment, producing more slender trees. Bending produced less slender trees through a combination of reduced height increment and increased diameter increment. Staking did not affect tree morphology. Trees under heavy shade were responsive to bending but were more slender and had lower bending resistance than unshaded trees with the same mechanical stimulus. These results point towards the biological basis for the development of tree instability in high density stands.
Comparative analysis of efficiency and productivity growth in Canadian regional boreal logging industries
Authors: Hailu Atakelty , Veeman Terrence S
Published: September 2003

The Canadian boreal logging industry has attracted little or no attention from economic researchers in spite of its importance for the competitiveness and long-term survival of other forest-based industries. This article uses a panel data set covering the period from 1977 to 1995 to analyze technical efficiency, technical change, and total factor productivity growth in the logging industries for six boreal provinces. The production technology is represented using a data envelopment analysis model. A transitive measure of productivity change that combines technical progress and changes in the degree of productive efficiency is computed. The empirical investigation reveals that logging activities in the boreal region are characterized by substantial efficiency differentials among the regions. Results from a Tobit analysis of efficiency differentials indicate that forest resource characteristics such as forest density and proportion of hardwood production were found to have positive effects. There was also evidence of significant positive scale effects. Engineering construction per area seems to be negatively related to efficiency. Total factor productivity in the boreal logging industry progressed at an average annual rate of 1.56%.
Physical and historical determinants of the pre- and post-settlement forests of northwestern Pennsylvania
Authors: Whitney Gordon G , DeCant Joseph P
Published: September 2003

Our analysis of the early land survey records and more recent U.S. Forest Service inventory data documents the changing nature of northwestern Pennsylvania's forests following European settlement. Initially, the northern portion of the four-county study area was dominated by forests of Fagus grandifolia Ehrh. and Acer saccharum Marsh. associated with the richer, finer-textured soils of the rolling Glaciated Appalachian Plateau. Up to 80% of the region was cleared for farming in the 19th century. Marginal farmland was abandoned and reverted to forests in the 20th century. Fires and leached, nutrient-poor soils favored the dominance of Quercus spp. and Castanea dentata (Marsh.) Borkh. in the presettlement forests of the rugged Unglaciated Appalachian Plateaus to the south. The rough nature of the terrain discouraged the early clearance of the plateaus' forests. The advent of the petroleum industry and its insatiable demand for barrels in the 19th century, however, assured the selective removal of the larger (>20 in. (50 cm) DBH) Quercus alba L. from the region's woods. The increasing homogeneity of northwestern Pennsylvania's forests today is due to the sharp decline of the more distinctive indicator species and the rise of a number of opportunistic old-field or gap species, notably Prunus serotina Ehrh. and Acer rubrum L.
Microbial biomass, nitrogen and phosphorus mineralization, and mesofauna in boreal conifer and deciduous forest floors following partial and clear-cut harvesting
Authors: Lindo Zoë , Visser Suzanne
Published: September 2003

The effects of partial and clear-cut harvesting on forest floor physical, chemical, and biological properties, forest floor mesofauna, and nutrient cycling were investigated in conifer- and deciduous-dominated stands of Alberta's mixedwood boreal forest. Forest floor samples were collected 2.5 years after harvest from clearcuts, strip-cut corridors in a partial cut, green tree retention patches in a partial cut, and uncut control sites. Partial cuts showed intermediate decreases in annual litter input and NH4-N between uncut and clear-cut sites of both the deciduous and conifer stands, as did microbial biomass, PO4-P, mesofauna abundance (total, Acari, and Collembola), and fine root biomass in the conifer stands. In the deciduous stands, microbial biomass and fine root biomass in partial- and clear-cut treatments were not significantly different, but were significantly reduced compared with the uncut controls. Mesofauna abundance was reduced in the corridors of the partial-cut treatment compared with partial-cut patch, clear-cut, and uncut treatments. In both deciduous and conifer stands, NO3-N was elevated in the partial-cut corridors and clearcuts compared with partial-cut patch and uncut treatments. Findings from this study show that negative impact to forest floor properties associated with clear-cut harvesting may be reduced in partial-cut harvesting systems.
Tree mortality and forest structure in the temperate rain forests of southeast Alaska
Authors: Hennon Paul E , McClellan Michael H
Published: September 2003

Tree mortality in 27 old-growth stands at three locales in southeast Alaska was evaluated to determine how types of tree death contributed to stand structure and the production of woody debris and to interpret small-scale disturbance. Basal area, density of stems, and the condition of dead trees were described for each tree species. Dead trees with broken boles were observed most frequently, followed by dead standing intact and uprooted trees. The frequencies of dead trees within snag and log deterioration classes indicated that most trees died standing and subsequently broke. Reconstructed annual mortality rates for overstory trees averaged 0.30.5%·year1for the three locales and were relatively stable through the previous century. Tree fall direction for both uprooted and broken trees aligned significantly with the downslope direction. All three types of tree mortality contributed substantially to structural diversity, reflecting a high degree of complexity associated with small-scale disturbance at these three study locales.
Genotype by environment interaction and its implications for genetic improvement of interior spruce in British Columbia
Authors: Xie C -Y
Published: September 2003

Ten-year height data from 232 open-pollinated interior spruce families tested in five seed planning zones located in north-central interior British Columbia were used to investigate the extent and pattern of genotype by environment (G×E) interaction and to examine the validity of the seed planning zone delineation in this region. The G×E interaction in the entire region was both statistically and practically significant, with an estimated type b genetic correlation coefficient of 0.64. The detected geographic pattern of the G×E interaction indicates that the old delineation is overly conservative, and consolidating the five old zones into the two new zones is a valid decision. A procedure was developed to convert the expected genetic gain, with respect to the old zone, to the new zone when seed from a rogued local seed orchard is used for reforestation in the entire new zone. A similar procedure was also proposed to predict the breeding value of an individual that was only tested in the old zone of its origin with respect to the new zone. Given the detected amounts of the G×E interaction, and considering other factors, using three to five sites in each new zone for the second-generation progeny testing seems to be appropriate.
Information technology and the newsprint demand in Western Europe: a Bayesian approach
Authors: Bolkesjø Torjus Folsland , Obersteiner Michael , Solberg Birger
Published: September 2003

This paper focuses on the impacts of new information technology on newsprint demand in a sample of West European countries (Germany, Italy, Spain, and the United Kingdom). It is hypothesized that information technology, through the ready and free availability of news content on the Internet, could induce a structural shift in the newsprint consumption pattern in these markets. Econometric analyses based on historical data for the four countries mentioned above do not yet support this hypothesis. Based on evidence from the United States, where Internet penetration is higher, and several recently published market studies, there is, however, reason to expect stagnating newsprint consumption in Western Europe. By using Bayesian demand models, we try to incorporate prior information from these market studies in the econometric analysis. A classical demand model, based solely on historical data from 1971 to 1999, is estimated for comparison with the Bayesian models. Predictions for newsprint consumption based on the Bayesian approach show lower future consumption levels than those predicted by the classical models, which are commonly used in forest product demand studies. We conclude that Bayesian models carry the potential to improve the quality of forest products demand analyses when a structural break can be expected and sufficient information on its dynamics is available.
The effects of soil fumigation on pine seedling production, weeds, foliar and soil nutrients, and soilborne microorganisms at a south Georgia (U.S.A.) forest tree nursery
Authors: Fraedrich Stephen W , Dwinell L David
Published: September 2003

Pine seedling production and pest problems were evaluated in plots fumigated with methyl bromide and nonfumigated plots over a 6-year period at a Georgia nursery. Fumigation increased bed densities for loblolly pine (Pinus taeda L.) in 1996 and slash pine (Pinus elliottii Engelm. var. elliottii) in 1998; differences were not observed between treatments in other years. The root collar diameter, height, and root and shoot masses of loblolly pine seedlings were often greater in fumigated plots during the first 3 years. Morphological characteristics rarely differed between treatments for slash pine. The primary pest problem was nutsedge (Cyperus spp.); most other weeds were controlled with herbicides used operationally at the nursery. Plant-parasitic nematode populations did not increase over time and were not a problem. Although Fusarium and Pythium spp. were more common in soil and on roots in nonfumigated plots, evidence of disease was rare. Fumigation increased the abundance of and changed the composition of Trichoderma spp. in soil and on roots. Soil manganese and iron, and foliar manganese, phosphorus, and nitrogen were greater in the fumigation treatment in some years. A better understanding of the risks of soilborne diseases may facilitate the development of pest management programs that are more cost-effective.