Simple Envelope Research Articles

Crown envelope shape measurements and models

This paper addresses tree crown envelope shape modeling from the perspective of optical passive remote sensing. The aims are 1) to review the specific requirements of crown shape models and ground measurement techniques in optical remote sensing, and 2) to present preliminary results from empirical, parametric crown shape and volume modeling of Scots pine and Norway spruce applicable in Finland. Results indicated that the basic dimensions (maximum radius, its height and crown length) of tree crowns were better predicted for pines, but the profile shape of the upper part of the crowns varied more than in spruce. Pine crowns were also slightly less concave than spruce crowns. No regularities were observed concerning the lower part of the crowns. The asymmetry of crowns increased as a function of tree age for both species, spruce crowns being more asymmetric than pine crowns. A comparison of measured crown volume with several simple geometrical crown shape envelopes showed that using a cone as a crown shape model for Scots pine and Norway spruce underestimates crown volume most severely. Other crown envelope shape models (e.g. ellipsoids) rendered crown volumes closer to the measured volume and did not differ considerably from each other.

The ZH ratio method for long-period seismic data: sensitivity kernels and observational techniques

SUMMARY Amplitude ratio between vertical and horizontal components of Rayleigh waves is controlled by structure beneath a seismic station. This ratio, measured as a function of frequency, has been extensively analysed for shallow crustal structure study in earthquake engineering and applied seismology. This quantity, termed the ZH ratio in this paper, may be useful for deep earth structure study and its feasibility for the frequency range between 0.004 and 0.05 Hz (period 20‐ 250 s) is explored in this paper. For depth sensitivity kernels, we demonstrate that a numerical approach is practical and provides sufficient accuracy for structural inversion. Depth extent of sensitivity kernels are about half of depth extent in phase velocity kernels, indicating that the ZH ratio is useful for studying the lithospheric structure. Two observational approaches for measurement of the ZH ratio are presented; the first approach uses simple envelope amplitude ratio and the second approach uses waveform correlation technique between vertical and horizontal components. The ZH ratio data alone only constrains structure beneath seismic stations but recent densification of seismic networks may make it possible to extend the analysis to regional scale structure. A greater opportunity may exist in combination of the ZH ratio method and the phase and group velocity measurements.

Responses of inferior colliculus neurons to double harmonic tones.

The auditory system can segregate sounds that overlap in time and frequency, if the sounds differ in acoustic properties such as fundamental frequency (f0). However, the neural mechanisms that underlie this ability are poorly understood. Responses of neurons in the inferior colliculus (IC) of the anesthetized chinchilla were measured. The stimuli were harmonic tones, presented alone (single harmonic tones) and in the presence of a second harmonic tone with a different f0 (double harmonic tones). Responses to single harmonic tones exhibited no stimulus-related temporal pattern, or in some cases, a simple envelope modulated at f0. Responses to double harmonic tones exhibited complex slowly modulated discharge patterns. The discharge pattern varied with the difference in f0 and with characteristic frequency. The discharge pattern also varied with the relative levels of the two tones; complex temporal patterns were observed when levels were equal, but as the level difference increased, the discharge pattern reverted to that associated with single harmonic tones. The results indicated that IC neurons convey information about simultaneous sounds in their temporal discharge patterns and that the patterns are produced by interactions between adjacent components in the spectrum. The representation is "low-resolution," in that it does not convey information about single resolved components from either individual sound.

Climate change and the genus <i>Rhipicephalus</i> (Acari : Ixodidae) in Africa

The suitability of present and future climates for 30 Rhipicephalus species in Africa are predicted using a simple climate envelope model as well as a Division of Atmospheric Research Limited-Area Model (DARLAM). DARLAM's predictions are compared with the mean outcome from two global circulation models. East Africa and South Africa are considered the most vulnerable regions on the continent to climate-induced changes in tick distributions and tick-borne diseases. More than 50% of the species examined show potential range expansion and more than 70% of this range expansion is found in economically important tick species. More than 20% of the species experienced range shifts of between 50 and 100%. There is also an increase in tick species richness in the south-western regions of the sub-continent. Actual range alterations due to climate change may be even greater since factors like land degradation and human population increase have not been included in this modelling process. However, these predictions are also subject to the effect that climate change may have on the hosts of the ticks, particularly those that favour a restricted range of hosts. Where possible, the anticipated biological implications of the predicted changes are explored.

Direct and indirect exciton states in GaAs-(Ga, Al)As double quantum wells under crossed electric and magnetic fields

A theoretical study of the direct and indirect exciton states in GaAs/Ga1-xAlxAs coupled double quantum wells under crossed electric and magnetic fields is presented. The setup of the system under consideration consists of an electric field perpendicular to the layers and an in-plane applied magnetic field. For calculations we use a variational procedure (by using a simple hydrogen-like envelope wave-function), in the effective-mass and parabolic-band approximations. Present theoretical results are found in fair agreement with available experimental measurements in double quantum well heterostructures under applied electric and magnetic fields.

Optical determination of the effective wetting layer thickness and composition inInAs∕Ga(In)Asquantum dots

A different approach to determining the wetting layer thickness and composition in $\mathrm{In}\mathrm{As}∕\mathrm{Ga}(\mathrm{In})\mathrm{As}$ quantum dot systems is proposed. This method combines the energy separation between heavy and light hole states determined experimentally and the results of a simple envelope function calculation to unambiguously obtain the wetting layer parameters. The heavy and light hole states are probed by photoluminescence excitation, but the proposed method can be extended to all absorptionlike measurements. For $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots, an effective wetting layer thickness of 3.6 monolayers and an average indium composition of 43% are obtained, in good agreement with results of structural characterization. Moreover, the optical transitions for InAs quantum dots covered by a $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick (Ga,In)As cap layer with indium content up to 20% have also been probed. Several transitions resulting from the quantum well formed by the wetting layer and the cap layer have been detected. Using the wetting layer parameters deduced for $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots, the calculated ${e}_{1}\text{\ensuremath{-}}{\mathit{hh}}_{1}$, ${e}_{1}\text{\ensuremath{-}}{\mathit{lh}}_{1}$, ${e}_{1}\text{\ensuremath{-}}{\mathit{hh}}_{2}$, and ${e}_{2}\text{\ensuremath{-}}{\mathit{hh}}_{2}$ transition energies correspond very well with the peak energies of the photoluminescence excitation spectra.

Exciton diamagnetic shift in [formula omitted] quantum wells under in-plane magnetic fields

Using a variational procedure in the effective-mass and parabolic-band approximations we investigate the effects of in-plane magnetic fields on the exciton states in single GaAs/Ga1-xAlxAs quantum wells. Exciton properties are analyzed by using a simple hydrogen-like variational envelope wave-function. Present theoretical results are compared with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of GaAs/Ga0.7Al0.3As quantum wells under in-plane magnetic fields [Phys. Rev. B 71 (2005) 045303].

Effects of crossed electric and magnetic fields on the electronic and excitonic states in bulk GaAs andGaAs∕Ga1−xAlxAsquantum wells

The variational procedure in the effective-mass and parabolic-band approximations is used in order to investigate the effects of crossed electric and in-plane magnetic fields on the electronic and exciton properties in semiconductor heterostructures. Calculations are performed for bulk GaAs and $\mathrm{Ga}\mathrm{As}∕{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ quantum wells, for applied magnetic fields parallel to the layers and electric fields in the growth direction, and it is shown that the combined effects on the heterostructure properties of the applied crossed electric and magnetic fields and the direct coupling between the center-of-mass and internal exciton motions may be dealt with via a simple parameter representing the spatial distance between the centers of the electron and hole magnetic parabolas. Exciton properties are analyzed by using a simple hydrogenlike envelope excitonic wave function and present theoretical results are found in fair agreement with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of $\mathrm{Ga}\mathrm{As}∕{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ quantum wells under in-plane magnetic fields.

Low-cost parametric test and diagnosis of RF systems using multi-tone response envelope detection

Because of aggressive technology scaling and multi-GHz operating frequencies of radio frequency (RF) devices, parametric failure test and diagnosis of RF circuitry is becoming increasingly important for the reduction of production test cost and faster yield ramp-up. A low-cost test and diagnosis method is proposed for multi-parametric faults in wireless systems that allows for the accurate prediction of the end-to-end specifications as well as the specifications of all the embedded RF modules. The procedure is based on application of an optimised test stimulus and extraction of its transient test response envelopes at RF signal nodes using a simple diode-based envelope detector. The test response is down-converted to lower frequencies compared to the operating frequency, thus eliminating the need to make RF measurements using expensive instrumentation. The specifications as well as the diagnostic information are computed from the test response of the envelope detector using statistical models. It is shown that the resulting information (features) in the transient envelope can accurately predict a host of test specifications using a single test configuration and test response capture event. Hardware measurement data from a 1.575 GHz transceiver shows that the test specifications of the system as well as the modules can be predicted with a high degree of accuracy using this method.

Determination of optical constants and inhomogeneity of optical films by two-step film envelope method

A simple two-step film envelope method has been proposed to determine the optical constants and small inhomogeneity of the optical films, which uses maximum envelopes and minimum envelope of the normal incidence transmittance of the two-step film. The two-step films were prepared by stopping the deposition process in the middle of the designed sputtering time, and then, after a full cooling down to room temperature, repeating the same deposition process again to complete the whole preparation of the films. The optical constants of Nb 2O 5–TiO 2 mixed films were calculated by two-step film envelope method and traditional envelope method. The experimental results demonstrate that the average refractive index and extinction coefficient calculated by two-step film envelope method are more accurate than those calculated by the traditional envelope method.

Cues for masked amplitude-modulation detection

The ability of psychoacoustic models to predict listeners' performance depends on two key stages: preprocessing and the generation of a decision variable. The goal of the current study was to determine the perceptually relevant decision variables in masked amplitude-modulation detection tasks in which the modulation depth of the masker was systematically varied. Potential cues were made unreliable by roving the overall modulation depth from trial to trial or were reduced in salience by equalizing the envelope energy of the standard and target after the signal was added. Listeners' performance was significantly degraded in both paradigms compared to the baseline (fixed-level modulation masker) condition, which was similar to those used in previous studies of masking in the envelope-frequency domain. Although this observation was broadly consistent with a simple long-term envelope power-spectrum model, there were several aspects of the data that were not. For example, the steep rate of change in threshold with masker depth and the fact that an optimal amount of envelope noise could enhance performance were not predicted by decision variables calculated directly from the stimulus envelope. A physiologically based processing model suggested a realistic nonlinear mechanism that could give rise to these second-order features of the data.

Design of simply structured robust controllers

A new method is presented for the design of simply structured multivariable controllers that can explicitly meet mixed sensitivity robust performance and robust stability criteria. Currently, most established robust controller design methods are synthesis-based and produce controllers that are often of much higher order than the plant. Based on the technique of diagonal dominance, this method proposes a novel means of directly ‘designing’ a robust controller, which among others, has the benefit that its order can be determined by the designer. By using elementary algebra, it is shown that the Gershgorin disks of a matrix may also be used to bind its singular values in addition to the eigenvalues. This fact is then exploited to create simple envelopes that bind the singular values of the sensitivity and complementary sensitivity functions, which are subsequently used in the design of the diagonal dominance-based controller such that the mixed criteria on the loop transfer function sensitivities may be met. As with other mixed sensitivity design techniques, this method does not guarantee that a controller is feasible for any set of arbitrary specifications. The method is applied to design a mixed-sensitivity controller for a mathematical model of the Rolls–Royce gas-turbine engine.

Analytic bond-order potential for predicting structural trends across thesp-valent elements

An analytic interatomic bond-order potential (BOP) is derived that depends explicitly on the group number of the $sp$-valent element. This is achieved by generalizing the previously published BOP for group-IV elements by extrapolating from half-full occupancy using a simple envelope function for the upper bound of the bond order. This interatomic potential predicts the structural trends across the $sp$-valent elements that are found by our tight-binding reference calculations and observed by experiment. Unlike empirical interatomic potentials this theoretically derived BOP includes the valence-dependent character of the bonding naturally within its remit.

Study of molecular layers in the atmosphere of the supergiant star μ Cep by interferometry in theKband

Infrared interferometry of supergiant and Mira stars has recently been reinterpreted as revealing the presence of deep molecular layers. Empirical models for a photosphere surrounded by a simple molecular layer or envelope have led to a consistent interpretation of previously inconsistent data. The stellar photospheres are found to be smaller than previously understood, and the molecular layer is much higher and denser than predicted by hydrostatic equilibrium. However, the analysis was based on spatial observations with medium-band optical filters, which mixed the visibilities of different spatial structures. This paper reports spatial interferometry with narrow spectral bands, isolating near-continuum and strong molecular features, obtained for the supergiant µ Cep. The measurements confirm strong variation of apparent diameter across the K-band. A layer model shows that a stellar photosphere of angular diameter 14.11±0.60 mas is surrounded by a molecular layer of diameter 18.56±0.26 mas, with an optical thickness varying from nearly zero at 2.15 µm to >1 at 2.39 µm. Although µ Cep and α Ori have a similar spectral type, interferometry shows that they differ in their radiative properties. Comparison with previous broad-band measurements shows the importance of narrow spectral bands. The molecular layer or envelope appears to be a common feature of cool supergiants.

100th Anniversary Special Paper: > On Hydrothermal Convection Systems and the Emergence of Life

Not only have submarine hydrothermal systems been responsible for a variety of mineral deposits, they may also have contributed to the emergence of life in the Hadean. Sulfide deposits can be precipitated where metalbearing hydrothermal solutions invade bacteriogenic H2S-bearing wet sediments and the overlying seawater or brine. Similarly, life might be viewed as a complex organic product that emerged when and where hydrothermal H2 and other reduced chemical species reacted with CO2 and other mildly oxidized molecules dissolved in the Hadean ocean. Semipermeable and semiconducting FeS barriers or membranes would have precipitated spontaneously where H2 and HS ‐ -bearing alkaline waters at ≤110°C seeped into the cool mildly acidic Fe-bearing Hadean ocean at a submarine hydrothermal mound on a ridge flank or on the deep ocean floor. The mound, consisting of Mg-rich clays, ephemeral carbonates, green rust, as well as the sulfides, acted as a natural, selfrestoring hydrothermal reactor. In particular, the sulfide barriers, composed of mackinawite and greigite, prevented the immediate titration of the two fluids and controlled their interactions. Metal sulfides were, and in tiny amounts are still, vital to all cells. Among other reactions they help catalyze the reduction of CO2 in autotrophic bacteria, including photosynthetic organisms. And the structure of greigite (NiFe5S8) is remarkably similar to the active sites (e.g., NiFe4S5) of the enzyme promoting the early metabolic pathway that generates acetate (CH3COO ‐ ) and H2O from CO2, H2, and a methyl group (-CH3). So clusters of greigite, sequestered in a simple organic envelope, could have acted as a protoenzyme, catalyzing the synthesis of acetate in the hydrothermal mound in the same way. Although, like “spent” ore fluid, most of the acetate and all of the water would have been lost to the Hadean ocean, an acetate fraction retained in microcavities within the mound could have combined to form the simple organic building blocks of life. Hydrothermal ammonia and minor cyanide also would have contributed to the synthesis of amino and nucleic acids. Traces of phosphorylated organic molecules, such as RNA (ribonucleic acid), would have adhered to mineral surfaces in the membranous barriers. Once their phosphates were bonded to such a surface, short RNA strands could have polymerized and provided a crude code for the assembly of variable sequences of amino acids (incipient proteins) generated in the same milieu. Alternatively, they could have replicated further RNA. Amino-acid sequences were a significant component of the first membranes and would have influenced membrane and cell survival. Once RNA codes for successful amino-acid sequences were passed on to daughter cells then life could be said to have emerged and evolution to have begun. Bacteria have flourished around hot springs ever since and on occasion have been responsible for the deposition of giant base metal sulfide deposits at or below the sea floor. Hence the study of life may be best begun by the study of those physico-chemical phenomena which result from the contact of two different liquids. Stephane Leduc 1911, p. xiv.

Neutron Star Crustal Interface Waves

The eigenfrequencies of nonradial oscillations are a powerful probe of a star's interior structure. This is especially true when there exist discontinuities such as at the neutron star (NS) ocean/crust boundary, as first noted by McDermott, Van Horn, & Hansen. The interface mode associated with this boundary has subsequently been neglected in studies of stellar nonradial oscillations. We revisit this mode, investigating its properties both analytically and numerically for a simple NS envelope model. We find that it acts like a shallow surface ocean wave, but with a large radial displacement at the ocean/crust boundary due to flexing of the crust with shear modulus μ P, the pressure. This displacement lowers the mode's frequency by a factor of ~(μ/P)1/2 ~ 0.1 in comparison to a shallow surface wave frequency on a hard surface. The interface mode may be excited on accreting or bursting NSs, and future work on nonradial oscillations should consider this mode. Our work also implies an additional mode on massive and/or cold white dwarfs with crystalline cores, which may have a frequency between the f-mode and g-modes, an otherwise empty part of the frequency domain.

Magnetic-field effects on quasi-two-dimensional excitons in coupledGaAs‐(Ga,Al)Asquantum wells

We have used the variational procedure in the effective-mass and nondegenerate parabolic band approximations in order to investigate the effects of a magnetic field on the exciton effective mass and dispersion in semiconductor heterostructures. Calculations are performed for bulk GaAs, and two-dimensional and quasi-two-dimensional excitons in coupled $\mathrm{Ga}\mathrm{As}\penalty1000-\hskip0pt(\mathrm{Ga},\mathrm{Al})\mathrm{As}$ quantum wells for applied magnetic fields perpendicular to the layers. A simple hydrogenlike envelope wave function provides the expected behavior for the exciton dispersion in a wide range of the center-of-mass momenta, and an analytical expression for the exciton effective mass is obtained. Present results lead to a magnetic-field dependent exciton effective mass and dispersion in quite good agreement with available experimental measurements in coupled $\mathrm{Ga}\mathrm{As}\penalty1000-\hskip0pt(\mathrm{Ga},\mathrm{Al})\mathrm{As}$ quantum wells.

Hidden Costs of Biodefense Research

Infectious diseases have threatened human civilization for more than 2000 yr. Hippocrates seems to have been the first observer to record an influenza pandemic in 412 B.C. (UW-Madison 2004). In addition, a major plague epidemic likely occurred in Egypt in 540, and then spread to Europe and Asia in the 14th century (Smith 1996-1997). The latter, known as the “Black Death,” devastated the peoples of the Old World on multiple occasions and is an oft-cited example of infectious disease. More insidious and equally profound in contemporary times has been the steady increase of human immunodeficiency virus, which now infects 38 million people, with 5 million new cases per year worldwide, and has caused 20 million deaths since its first diagnosis (UN AIDS 2004). Malaria afflicts 300 million people globally, with 1 to 1.5 million deaths annually (WHO 2004). Yet these statistics pale in comparison with tuberculosis, from which one third of the world population is infected, with 2 to 3 million deaths annually, and antibiotic-resistant tuberculosis is on the increase (WHO 2004). The influenza pandemic of 1918 occurred on a global scale and resulted in 40 million deaths. It was the most devastating epidemic in world history, and the origin of the 1918 virus remains undetermined. What is known is that epidemics of influenza occur annually, and the likelihood of another pandemic is certain (Reid and Taubenberger 2003). Recent outbreaks of severe acute respiratory syndrome (SARS) elicit concern that a similar event might occur with this newly emergent zoonotic coronavirus. Of the last 12 emerging infectious diseases, 11 have been zoonotic, or transmitted from animals to people (F. A. Murphy, University of California-Davis, personal communication, 2004). Increasing populations, poverty, politics, religious zealotry, despair, travel, environmental degradation, intensive farming, and many other factors are creating a virtual “witches brew” of opportunity for emerging and re-emerging pathogens. Iatrogenic introduction (a.k.a. bioterrorism) is simply another means of transmission and spread of infectious agents, which, in the current political climate, evokes considerable fear among the populace. Through the dark side of the human condition, pathogens can now be elegantly engineered genetically, although in many cases, this process is not necessary because relatively primitive means can be used to utilize them for malicious intent. Bioterrorism, which was on the agenda of the cold war for decades, has taken on totally new dimensions with the realization that the geopolitics of detente between super powers can no longer contain the possibility of a bioterrorist event from happening. The US anthrax scare showed us that a simple anonymous postal envelope can serve as a fomite of terror. Remarkably, 22 cases and five deaths from anthrax, which are certainly not trivial, have effectively terrorized the politics of research in the United States, and in many ways have overshadowed the much more sobering but paradoxically accepted terror of AIDs, tuberculosis, malaria, influenza, and emerging and re-emerging infectious diseases. The National Institutes of Health (NIH), which was established in 1949, has been an American success story. It fostered innovative research and individual initiative within the scientific community, which in turn created a vital biomedical research infrastructure for academia, including robust scientific environments for training the next generation of scientists in hypothesis-driven research. The system allowed funding of a broad range of subjects, with peer review and funding based on merit and relatively unencumbered by politics. This broad base of science fostered interdisciplinary discovery as research results were openly published in peer-reviewed journals. Advances in one field often fostered advances in others. Congress recognized the enormous impact of NIH-funded research on both the economy and the health of the nation, with unprecedented bipartisan support that resulted in doubling of the NIH budget over the last 5 yr. This investment has ended, and the modest increases that are projected for the NIH budget cannot keep pace with increasing costs of performing science, sustaining excellence, and solving complex diseases that require basic research. Those days are indeed over, and they ended even more abruptly after September 11, 2001. Almost immediately, $1.7 billion became available for biodefense research. The Stephen W. Barthold, D.V.M., Ph.D., is a Professor in the Department of Comparative Medicine, University of California, Davis, and a member of the Institute of Medicine.

UWB direct chaotic communication technology

In this letter, an ultra-wideband (UWB) direct chaotic communication technology is proposed. Based on this system, a 2-GHz wide chaotic signal is directly generated into the lower band of the UWB spectrum, i.e., 3.1-5.1 GHz. The information component is modulated by the chaotic signal based on the chaotic-on-off keying modulation scheme which results in a series of chaotic radio pulses. At the receiver, a simple noncoherent envelope detector is used as an energy collector. Various system design parameters and tradeoffs are discussed in the letter in order to meet the low-complexity, low-power consumption, and low-cost requirements while still compliant with the Federal Communications Commission UWB regulation. The average power consumptions for various operating data rates and the technical feasibilities of implementing the above system as low-cost integrated circuit are also addressed. Additionally, the system performance in both additive white Gaussian noise (AWGN) channel and various types of multipath channels are provided in order to further demonstrate the capability of the proposed system.

Stresses in the subducting slab beneath southwest Japan and relation with plate geometry, tectonic forces, slab dehydration, and damaging earthquakes

We infer stresses in the subducting slab beneath southwest Japan from focal mechanisms and discuss their geodynamical implications. The majority of the 824 fault plane solutions used in this study were obtained by the Japan Meteorological Agency for earthquakes that occurred during 1970–2002 and were previously unpublished. The focal mechanisms are believed to reflect stresses in both the untransformed slab crust and the slab mantle. The stresses are controlled by tectonic forces, and the earthquakes are facilitated by local dehydration. The slab experiences a regional E–W stretch, that is, downdip and margin‐parallel tension at the Kyushu and Nankai margins, respectively. We propose that the margin‐parallel component of mantle resistance to the obliquely subducting young slab at Nankai provides an easterly stretch, acting against the westerly slab pull of the older and colder part of the slab at northern Kyushu. Despite the complex slab geometry along the Nankai margin the direction of tension is largely parallel with the local strike of the slab, indicating that the slab is a stress guide. The complex slab geometry is not related to the present stress regime but likely reflects severe deformation in the past when an extremely young and incompetent plate was forced to subduct against its own buoyancy. The maximum margin‐parallel stretch and a sharp bending of the slab both occur in the area of the 2001 M 6.7 Geiyo earthquake. Using a simple strength envelope model, we demonstrate that normal‐faulting failure of the slab mantle can occur under such conditions.