Log Period Research Articles

Impacts of logging on the canopy and the consequences for forest management in French Guiana

This study aimed to correlate logging intensity with canopy opening using medium-resolution satellite images (SPOT-type) on a sample of 15 blocks totaling more than 3300ha in two French Guianan forests with different reliefs. The maps obtained show the cumulative impacts on the canopy over the entire logging period (2008–2010). The percentages of canopy openness and the unit areas per logged tree were examined with logging statistics and GPS mappings of felled stems for 4 sub-samples. At the block scale, a 20% canopy opening after logging was observed for a logging intensity of 3.5treesha−1. The average canopy opening size per harvested tree was 601m2, which included felling gaps and openings resulting from the construction of roads and trails needed to remove the timber. The coefficients of variation of these variables were low. General linear models (glm) were created to test the relationship between canopy damage, logging intensity and relief at local scales (1 and 4ha) and at the management unit scale (i.e. 200–300ha). The model created at management-unit level (block level) did not detect any significant effect of the variables on the percentage of canopy openness. However, a significant and concordant relationship was demonstrated at local levels between relief, logging intensity, their interaction on the one hand and the percentage of canopy openness on the other. A maximum local harvesting intensity of 8 trees per hectare on plateaus makes it possible to obtain an opening of less than 33% at an 85% probability threshold. In contrast, the same canopy openness threshold is obtained at only 5 trees per hectare on hillier terrain, which suggests that it would be advantageous to adjust silviculture recommendations according to forest landscape. The average openness of 20% observed in this sample, considered in relation to the cutting cycle in effect in French Guiana (65years), implies a complete renewal of forest stands after 325years, assuming multifunctional management objectives.

Properties of CFTs dual to charged BTZ black hole

We study properties of strongly coupled CFT's with non-zero background electric charge in 1 + 1 dimensions by studying the dual gravity theory—which is a charged BTZ black hole. Correlators of operators dual to scalars, gauge fields and fermions are studied at both T = 0 and T ≠ 0 . In the T = 0 case we are also able to compare with analytical results based on AdS 2 and find reasonable agreement. In particular the correlation between log periodicity and the presence of finite spectral density of gapless modes is seen. The real part of the conductivity (given by the current–current correlator) also vanishes as ω → 0 as expected. The fermion Green's function shows quasiparticle peaks with approximately linear dispersion but the detailed structure is neither Fermi liquid nor Luttinger liquid and bears some similarity to a “Fermi–Luttinger” liquid. This is expected since there is a background charge and the theory is not Lorentz or scale invariant. A boundary action that produces the observed non-Luttinger liquid like behavior ( k-independent non-analyticity at ω = 0 ) in the Green's function is discussed.

Прогнозирование продолжительности периода разработки зимних лесосек в условиях Республики Коми

Прогнозирование продолжительности периода разработки зимних лесосек в условиях Республики Коми

Discrete self-similarity in type-II strong explosions

We present new solutions to the strong explosion problem in a nonpower law density profile. The unperturbed self-similar solutions discovered by Waxman and Shvarts describe strong Newtonian shocks propagating into a cold gas with a density profile falling off as r−ω, where ω>3 (type-II solutions). The perturbations we consider are spherically symmetric and log periodic with respect to the radius. While the unperturbed solutions are continuously self-similar, the log periodicity of the density perturbations leads to a discrete self-similarity of the perturbations, i.e., the solution repeats itself up to a scaling at discrete time intervals. We discuss these solutions and verify them against numerical integrations of the time dependent hydrodynamic equations. Finally we show that this method can be generalized to treat any small, spherically symmetric density perturbation by employing Fourier decomposition.

A Lumped-Circuit Model for a Triband Trapped Dipole Array-Part 1: Model Description

Demands on emergency radio frequency (RF) links have shown how important high-frequency (HF) (330 MHz) communications can be for medium to long range. The YagiUda and the log period antenna are among some of the more popular HF antennas. The KLM's Communications Equipment, Inc., four-element KT-34A antenna is based on both types of antennas and operates in the 10-, 15-, and 20-m bands. It relies on parallel LC-circuits acting as traps to form three desired element lengths. A lumped-circuit model of this type of antenna has been developed based on the dimensions in the original manual. In part 1 we tune this numerical model to approximate the KT-34A and use it to investigate performance over an imperfect ground plane.

DESIGN AND SIMULATION OF CIRCULAR ARRAYS OF TRAPEZOIDAL-TOOTH LOG-PERIODIC ANTENNAS VIA GENETIC OPTIMIZATION

Circular arrays of log-periodic (LP) antennas are designed and their operational properties are investigated in a sophisticated simulation environment that is based on the recent advances in computational electromagnetics. Due to the complicated structures of the trapezoidal-tooth array elements and the overall array configuration, their analytical treatments are prohibitively difficult. Therefore, the simulation results presented in this paper are essential for their analysis and design. We present the design of a threeelement LP array showing broadband characteristics. The directive gain is stabilized in the operation band using optimization by genetic algorithms. We demonstrate that the optimization procedure can also be used to provide beam-steering ability to LP arrays.

Modeling and synthesis of circular‐sectoral arrays of log‐periodic antennas using multilevel fast multipole algorithm and genetic algorithms

Circular‐sectoral arrays of log‐periodic (LP) antennas are presented for frequency‐independent operation and beam‐steering capability. Specifically, nonplanar trapezoidal tooth LP antennas are considered in a circular array configuration, where closely spaced antennas occupy a sector of the circle. Electromagnetic interactions of the array elements, each of which is a complicated LP antenna structure, are rigorously computed with the multilevel fast multipole algorithm (MLFMA). Genetic algorithms (GAs) are also employed in combination with MLFMA for synthesis and design purposes. By optimizing the excitations of the array elements via GAs, beam‐steering ability is achieved in addition to the broadband (nearly frequency‐independent) characteristics of the designed arrays. Computational results are presented to demonstrate the important properties of LP arrays.

Multivariate comparisons of the period-light-curve shape distributions of Cepheids in five galaxies

A number of published tests suitable for the comparison of multivariate distributions are described. The results of a small power study, based on realistic Cepheid log period ‐ Fourier coefficient data, are presented. It is found that a statistic due to Henze has good general performance. The tests are applied to Cepheid observations in the Milky Way galaxy, Large Magellanic Cloud, Small Magellanic Cloud, IC 1613 and NGC 6822. The null hypothesis of equal populations is rejected for all pairs compared, except IC 1613 ‐ NGC 6822.

Effects of Logging Second‐Growth Forests on Headwater Populations of Coastal Cutthroat Trout: A 6‐Year, Multistream, Before‐and‐After Field Experiment

AbstractTo understand how logging of second‐growth forests affects populations of coastal cutthroat trout Oncorhynchus clarkii clarkii, we examined trout relative abundance, body condition (mass relative to length), and physical and thermal habitat in the summer and winter in four headwater streams (two treatment streams and two nonlogged control streams) over a 6‐year period (2 years prelogging [1997–1998] and 4 years postlogging [1999–2002]). This is one of the first efforts to conduct a multiyear, replicated stream, before‐and‐after experiment on this scale to assess the effects of logging on fish and habitat. In the treatment streams, 21% of the watershed area was logged by clear‐cutting (no scarification or slash‐burning). Careful logging approaches were employed to remove most of the riparian overstory (i.e., no machines were used within 5 m of stream, logs were felled and yarded away from riparian zones, all shrubs were left behind, and large wood was left in streams). Because a cooler summer climate occurred coincidentally with our postlogging period (the mean daily average summer air temperature was 1–2°C cooler than the temperature during the prelogging period), the mean average and mean maximum daily stream temperatures declined after the logging period in the control streams and remained the same in the treatment streams. After accounting for the effects of climate, logging had warmed treatment streams by about 1°C. We could not detect any logging treatment effects on summer or winter relative abundance or condition, nor were any changes evident to instream physical habitat associated with the logging treatment. These results were probably attributable to the careful logging approaches employed and the cooler climate that occurred during the postlogging period.

Consequences of aggregation for the trace element distribution in the subsoil of a Planosol naturally rich in trace metal

Element distribution at the aggregate scale was studied in a soil naturally rich in trace elements. The studied soil was a Planosol developed in gneiss parent material (Massif Central, France) that exhibits a well-structured clayey pedological (B) horizon. This horizon was sampled for aggregates that showed a strong differentiation between an inner part and an outer part. Element distribution in these aggregates was studied (1) after manual separation of their inner and outer parts; (2) on aggregate thin sections after polyester resin impregnation. The concentrations of trace and major elements and the main mineralogical phases (X-ray diffraction) were determined on the two fractions. Chemical speciation of TEs was also performed on these fractions. Thin sections were observed by optical and scanning electron microscopy and major elements were mapped by electron microprobe. Manual fractionation and electron microprobe mapping showed a clear differentiation in element distribution between the inner and outer parts of the aggregates. The inner part was richer in Fe, Cu, Ni, Co, Al, K and Mn than the outer one. This last one was however richer in Si. Extractions showed that this distribution is explained by the presence of silicate minerals rich in TEs and by the larger amount of oxides in the inner part of the aggregate compared to the outer part which was richer in coarse sand, mainly quartz. Microscopic studies also showed that the inner part was rather complex. Pores surroundings were also depleted in Fe and enriched in Si as aggregate outer parts. This uneven distribution was most likely the result of two different mechanisms: (1) input of material coming from the upper horizons due to swelling and shrinking according to seasonal changes; and (2) preferential weathering of the outer part of aggregates due to preferential flow during the water logging period in winter. This differentiation was especially marked for Co, Zn and Cu and was linked to oxide dynamics.

A Bayesian analysis of log-periodic precursors to financial crashes

A large number of papers have been written by physicists documenting an alleged signature of imminent financial crashes involving so-called log-periodic oscillations–oscillations which are periodic with respect to the logarithm of the time to the crash. In addition to the obvious practical implications of such a signature, log-periodicity has been taken as evidence that financial markets can be modelled as complex statistical-mechanics systems. However, while many log-periodic precursors have been identified, the statistical significance of these precursors and their predictive power remain controversial in part because log-periodicity is ill-suited for study with classical methods. This paper is the first effort to apply Bayesian methods in the testing of log-periodicity. Specifically, we focus on the Johansen–Ledoit–Sornette (JLS) model of log periodicity. Using data from the S&P 500 prior to the October 1987 stock market crash, we find that, if we do not consider crash probabilities, a null hypothesis model without log-periodicity outperforms the JLS model in terms of marginal likelihood. If we do account for crash probabilities, which has not been done in the previous literature, the JLS model outperforms the null hypothesis, but only if we ignore the information obtained by standard classical methods. If the JLS model is true, then parameter estimates obtained by curve fitting have small posterior probability. Furthermore, the data set contains negligible information about the oscillation parameters, such as the frequency parameter that has received the most attention in the previous literature.

Nonplanar trapezoidal tooth log‐periodic antennas: Design and electromagnetic modeling

Nonplanar trapezoidal tooth log‐periodic (LP) antennas are investigated by combining the wisdom of theoretical design procedures with the power of accurate numerical simulation environments. Once the theoretical design is completed, electromagnetic simulations employing accurate integral equation solvers are utilized to test and correct the original design. A two‐element array of trapezoidal tooth LP antennas is designed. The array features beam‐steering ability as a novelty, in addition to frequency independence and higher directivity. Beam steering is achieved by optimizing the excitation coefficients of the two LP antennas.

Bosons with multifractal energy spectrum: specific heat log periodicity and Bose–Einsteincondensation

The thermodynamics for systems of non-interacting bosons with multifractal energyspectrum is considered. The critical attractors of one-dimensional generalized logisticand circular maps are used to generate multifractal bounded spectra with welldefined scaling exponents. The specific heat is then calculated for both cases ofconserved and non-conserved particle number, showing a power-law behaviourwhich is modulated by log-periodic oscillations when the energy spectrum is notdense. The occurrence of Bose–Einstein condensation for systems with conservedparticle number, at which the specific heat is discontinuous, is also analyzed.

Investigation of a Broad-Band Cavity-Backed Array Antenna

A new multimode antenna consisting of a circular array of log periodic (LP) elements, suspended in dielectric material and placed in a circular cavity with a conical bottom, is presented and discussed. The conducting elements are contained within the dielectric. Far field patterns obtained using the method of moments (MoM) are compared to experimental measurements and show good agreement for both magnitude and phase. The effect of cavity cone angle on the antenna patterns is presented. Careful selection of the cone angle can result in significant suppression of undesirable higher order resonant modes on the LP elements.

The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves Is the Oosterhoff-Arp-Preston Period Ratio Effect in Disguise

The correlation of particular Fourier components of the light curves of RR Lyrae variables with metallicity, discovered by Simon and later by Kovacs and his coworkers, is shown to have the same explanation as the period ratios (period shifts in log P) between RRab Lyrae variables that have the same colors, amplitudes, and light-curve shapes but different metallicities. A purpose of this paper is to demonstrate that the model which predicts the period-metallicity relations is the mediating parameters of colors, amplitudes, and light-curve shapes also explains the Simon/Kovacs et al. correlation between period, Phi_31, and metallicity. The proof is made by demonstrating that the combination of the first and third phase terms in a Fourier decomposition of RRab light curves, called Phi_31 by Simon and Lee, varies monotonically across the RR Lyrae instability strip in the same way that amplitude, color, and rise time vary with period within the strip. The premise of the model is that if horizontal branches at the RR Lyrae strip are stacked in luminosity according to the metallicity, then there necessarily must be a log period shift between RR Lyraes with different metallicities at the same Phi_31 values. However, there are exceptions to the model. (...)

What Fraction of Sun‐like Stars Have Planets?

The radial velocities of ~1800 nearby Sun-like stars are currently being monitored by eight high-sensitivity Doppler exoplanet surveys. Approximately 90 of these stars have been found to host exoplanets massive enough to be detectable. Thus, at least ~5% of target stars possess planets. If we limit our analysis to target stars that have been monitored the longest (~15 years), ~11% possess planets. If we limit our analysis to stars monitored the longest and whose low surface activity allows the most precise velocity measurements, ~25% possess planets. By identifying trends of the exoplanet mass and period distributions in a subsample of exoplanets less biased by selection effects and linearly extrapolating these trends into regions of parameter space that have not yet been completely sampled, we find that at least ~9% of Sun-like stars have planets in the mass and orbital period ranges M sin i > 0.3MJup and P < 13 years and at least ~22% have planets in the larger range M sin i > 0.1MJup and P < 60 years. Even this larger area of the log(mass)-log(period) plane is less than 20% of the area occupied by our planetary system, suggesting that this estimate is still a lower limit to the true fraction of Sun-like stars with planets, which may be as large as ~100%.

A method for QT correction based on beat-to-beat analysis of the QT/RR interval relationship in conscious telemetred beagle dogs

Introduction: Drug-induced QT prolongation is a major clinical risk factor for arrhythmia induction, particularly torsades de pointes. QT interval is rate dependent, and many formulae exist that attempt to correct QT for changes in heart rate. Most correction factors are acknowledged to overcorrect at high heart rates, undercorrect at low heart rates, and tend to be species specific. Data collected from computerised data acquisition systems are normally reported as means over a given logging period, and so extremes of heart rate are averaged out. Therefore, the aim of this study was to develop a technique for assessing drug-induced changes in the QT/RR relationship, which is simple, suitable for small group sizes, and better able to determine rate-dependent effects of drugs. Methods: Telemetred beagle dogs ( n=4) instrumented for the measurement of electrocardiogram (ECG) were monitored for four separate 20-h periods to define the control QT/RR relationship. Data were binned by RR interval, in 10 ms bins, to produce a control curve. Each dog was treated with vehicle and sotalol (4, 8, 32 mg/kg) in a crossover design to determine whether drug-induced changes in the QT/RR relationship could be detected using the data binning technique. Results: The control QT/RR relationship was curvilinear with a steep section for RR intervals below 580 ms, and was much less steep after this point. Sotalol produced QT prolongation and bradycardia—Fridericia's correction (QTf) reduced the magnitude of this prolongation. The data analysed by the binning technique showed a larger prolongation in QT than was suggested by QTf, and an inverse frequency-dependent response. Discussion: Beat-to-beat analysis and binning allows accurate determination of the QT/RR relationship and assessment of QT prolongation without recourse to mathematical modelling. It also highlights the importance of assessing QT effects in well-trained animals over a range of heart rates.

Planar Log-Periodic Antennas on Extended Hemishperical Silicon Lenses for Millimeter/Submillimeter Wave Detection Applications

In this paper, the radiation properties of log-periodic (LP) antennas on extended hemispherical dielectric lenses are investigated. The starting point is the far field pattern for the log-periodic antenna on a semi-infinite silicon substrate obtained from numerical simulation. Then the effects of extended hemispherical silicon dielectric lenses on this far field pattern are evaluated using ray tracing and field integration techniques. The far fields patterns out of the lenses are derived as a function of the extension length (L), from which the optimum L can be determined. The coupling efficiencies of the pattern to Gaussian beams are also calculated. The computation results show that the log-periodic antennas have good performance in terms of impedance and pattern and can be used in many submillimeter/THz systems. The simulation methods are verified by comparing the simulation results with experimental data from literature. The utilized approach represents an effective method for log periodic antenna-lens system design at millimeter/submillimeter wavelengths.

The Frequency of Binary Stars in the Core of 47 Tucanae

Differential time series photometry has been derived for 46,422 main-sequence stars in the core of 47 Tucanae. The observations consisted of near-continuous 160 s exposures alternating between the F555W and F814W filters for 8.3 days in 1999 July with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Using Fourier and other search methods, 11 detached eclipsing binaries and 15 W Ursa Majoris stars have been discovered plus an additional 10 contact or near-contact noneclipsing systems. After correction for nonuniform area coverage of the survey, the observed frequencies of detached eclipsing binaries and W UMa stars within 90'' of the cluster center are 0.022% and 0.031%, respectively. The observed detached eclipsing binary frequency, the assumptions of a flat binary distribution with log period, and assuming that the eclipsing binaries with periods longer than about 4 days have essentially their primordial periods imply an overall binary frequency of 13% ± 6%. The observed W UMa frequency and the additional assumptions that W UMa stars have evolved to contact according to tidal circularization and angular momentum loss theory and that the contact binary lifetime is 109 yr imply an overall binary frequency of 14% ± 4%. An additional 71 variables with periods from 0.4 to 10 days have been found, which are likely to be BY Draconis stars in binary systems. The radial distribution of these stars is the same as that of the eclipsing binaries and W UMa stars and is more centrally concentrated than average stars but less so than the blue straggler stars. A distinct subset of six of these stars falls in an unexpected domain of the color-magnitude diagram, comprising what we propose to call red stragglers.

Use of global positioning system technology to track subject's location during environmental exposure sampling.

Global positioning system (GPS) data recorders were worn by subjects in the Oklahoma Urban Air Toxics Study (OUATS) for automatic logging of their location as they went about their normal daily activities. The location information obtained by the GPS units had an uncertainty of about 10-20 m, which was sufficiently precise to track subjects' movements on trips outside the immediate vicinity of their homes. Due to instrument problems, primarily related to reduced battery life, the units operated for only about 30% of the total monitoring time attempted in 25 trials. The GPS data were compared to time-activity diaries kept by the subjects. In almost all cases, the GPS data confirmed all travel events reported in the subjects' diaries. Additionally, in five out of five trials in which the logging period covered most or all of the subjects' daytime activities, at least one travel event that was not recorded in the diary was detected by GPS. Notwithstanding the limitations of present technology, GPS was found to be a promising means for tracking of research subjects in community-based exposure assessment studies.