Mean Extinction Research Articles

Colloquium paper: how many tree species are there in the Amazon and how many of them will go extinct?

New roads, agricultural projects, logging, and mining are claiming an ever greater area of once-pristine Amazonian forest. The Millennium Ecosystems Assessment (MA) forecasts the extinction of a large fraction of Amazonian tree species based on projected loss of forest cover over the next several decades. How accurate are these estimates of extinction rates? We use neutral theory to estimate the number, relative abundance, and range size of tree species in the Amazon metacommunity and estimate likely tree-species extinctions under published optimistic and nonoptimistic Amazon scenarios. We estimate that the Brazilian portion of the Amazon Basin has (or had) 11,210 tree species that reach sizes >10 cm DBH (stem diameter at breast height). Of these, 3,248 species have population sizes >1 million individuals, and, ignoring possible climate-change effects, almost all of these common species persist under both optimistic and nonoptimistic scenarios. At the rare end of the abundance spectrum, however, neutral theory predicts the existence of approximately 5,308 species with <10,000 individuals each that are expected to suffer nearly a 50% extinction rate under the nonoptimistic deforestation scenario and an approximately 37% loss rate even under the optimistic scenario. Most of these species have small range sizes and are highly vulnerable to local habitat loss. In ensembles of 100 stochastic simulations, we found mean total extinction rates of 20% and 33% of tree species in the Brazilian Amazon under the optimistic and nonoptimistic scenarios, respectively.

Stochastic niche structure and diversity maintenance in the T cell repertoire

The reliability of the immune response to pathogenic challenge depends critically on the size and diversity of the T cell repertoire. We study naïve T cell repertoire diversity maintenance by a stochastic model that incorporates the concept of competition between T cells for survival stimuli emanating from self-antigen presenting cells (APCs). In the mean field approximation we show that clonotype extinction is certain and compute mean extinction times. We introduce the concept of mean niche overlap and show that clones with a mean niche overlap greater than one have a short repertoire lifespan. This selection differential induces minimal recognition commonality between T cell receptors (TCRs) resulting in a diverse T cell repertoire.

Temperature and pressure dependent effective thermal conductivity of fibrous insulation

In present paper, a numerical model combined radiation and conduction heat transfer was developed to predict the effective thermal conductivity of fibrous insulation at various temperatures and pressures. Effective thermal conductivities of the fibrous insulation were measured over a wide range of temperature (300–973 K) and pressure ( 10 −2 – 10 5 Pa ) using a developed apparatus. The transmittance spectra in the wavelength range of 2.5–25 μm were also measured at temperatures up to 973 K using a Fourier Transform Infrared Spectrometer. From transmittance data, the spectral extinction coefficients and Rosseland mean extinction coefficients were obtained at various temperatures to investigate the radiative heat transfer in fibrous insulation. The numerical and experimental data were compared. It was found that the calculated values corresponded with the experimental values within an average of 14.7 percent. Numerical results were consistent with experimental results throughout the investigated environmental conditions.

Extinction of an infectious disease: A large fluctuation in a nonequilibrium system

We develop a theory of first passage processes in stochastic nonequilibrium systems of birth-death type using two closely related epidemiological models as examples. Our method employs the probability generating function technique in conjunction with the eikonal approximation. In this way the problem is reduced to finding the optimal path to extinction: a heteroclinic trajectory of an effective multidimensional classical Hamiltonian system. We compute this trajectory and mean extinction time of the disease numerically and uncover a nonmonotone, spiral path to extinction of a disease. We also obtain analytical results close to a bifurcation point, where the problem is described by a Hamiltonian previously identified in one-species population models.

Implications for Galaxy Evolution from Cosmic Evolution of the Supernova Rate Density

Abstract We report on a comprehensive statistical analysis of observational data of the cosmic evolution of the supernova (SN) rate density, to derive constraints on cosmic star-formation history and the nature of a type Ia supernova (SNIa) progenitor. We use all available information concerning the magnitude, SN type, and redshift information of both type Ia and core-collapse (CC) SNe in GOODS and SDF, as well as SNIa rate densities reported in the literature. We also add 157 SN candidates in the past Subaru/Suprime-Cam data that are newly reported here, to increase the statistics. We find that the current data set of the SN rate density evolution already gives a meaningful constraint on the evolution of the cosmic star formation rate (SFR) at $z \lesssim 1$, though strong constraints cannot be derived for the delay time distribution (DTD) of SNe Ia. We derive a constraint of $\alpha \sim $ 3–4 [the evolutionary index of SFR density $\propto (1+z)^\alpha$ at $z \lesssim 1$] with evidence for a significant evolution of the mean extinction of CC SNe [$E(B-V) \sim$0.5 at $z \sim$0.5 compared with $\sim 0.2$ at $z=0$], which does not change significantly within a reasonable range of various DTD models. This result is consistent with the systematic trend of $\alpha $ estimates based on galactic SFR indicators at different wavelengths (ultraviolet, H$\alpha $, and infrared), indicating that there is a strong evolution in the mean extinction of star-forming regions in galaxies at relatively low redshift range of $z \lesssim$0.5. These results are obtained by a method that is completely independent of galaxy surveys and, especially, there is no detection limit about the host galaxy luminosity in our analysis, giving a strong constraint on the star-formation activity in high-$z$ dwarf galaxies or intergalactic space.

Photometric redshifts in the SWIRE Survey

We present the SWIRE Photometric Redshift Catalogue 1 025 119 redshifts of unprecedented reliability and of accuracy comparable with or better than previous work. Our methodology is based on fixed galaxy and quasi-stellar object templates applied to data at 0.36–4.5 μm, and on a set of four infrared emission templates fitted to infrared excess data at 3.6–170 μm. The galaxy templates are initially empirical, but are given greater physical validity by fitting star formation histories to them, which also allows us to estimate stellar masses. The code involves two passes through the data, to try to optimize recognition of active galactic nucleus (AGN) dust tori. A few carefully justified priors are used and are the key to supression of outliers. Extinction, A_V , is allowed as a free parameter. The full reduced χ^2_ν (z) distribution is given for each source, so the full error distribution can be used, and aliases investigated. We use a set of 5982 spectroscopic redshifts, taken from the literature and from our own spectroscopic surveys, to analyse the performance of our method as a function of the number of photometric bands used in the solution and the reduced χ^2_ν . For seven photometric bands (5 optical + 3.6, 4.5 μm), the rms value of (z_(phot)−z_(spec)/(1 +z_(spec) is 3.5 per cent, and the percentage of catastrophic outliers [defined as >15 per cent error in (1 +z)], is ∼1 per cent. These rms values are comparable with the best achieved in other studies, and the outlier fraction is significantly better. The inclusion of the 3.6- and 4.5-μm IRAC bands is crucial in supression of outliers. We discuss the redshift distributions at 3.6 and 24 μm. In individual fields, structure in the redshift distribution corresponds to clusters which can be seen in the spectroscopic redshift distribution, so the photometric redshifts are a powerful tool for large-scale structure studies. 10 per cent of sources in the SWIRE photometric redshift catalogue have z > 2, and 4 per cent have z > 3, so this catalogue is a huge resource for high-redshift galaxies. A key parameter for understanding the evolutionary status of infrared galaxies is L_(ir)/L_(opt) . For cirrus galaxies this is a measure of the mean extinction in the interstellar medium of the galaxy. There is a population of ultraluminous galaxies with cool dust and we have shown SEDs for some of the reliable examples. For starbursts, we estimate the specific star formation rate, φ_*/M_* . Although the very highest values of this ratio tend to be associated with Arp220 starbursts, by no means all ultraluminous galaxies are. We discuss an interesting population of galaxies with elliptical-like spectral energy distributions in the optical and luminous starbursts in the infrared. For dust tori around type 1 AGN, L_(tor)/L_(opt) is a measure of the torus covering factor and we deduce a mean covering factor of 40 per cent. Our infrared templates also allow us to estimate dust masses for all galaxies with an infrared excess.

Noise Enhanced Persistence in a Biochemical Regulatory Network with Feedback Control

We find that discrete noise of inhibiting (signal) molecules can greatly delay the extinction of plasmids in a plasmid replication system: a prototypical biochemical regulatory network. We calculate the probability distribution of the metastable state of the plasmids and show in this example that the reaction rate equations may fail in predicting the average number of regulated molecules even when this number is large, and the time is much shorter than the mean extinction time.

Anomalous finite-size effects in the Battle of the Sexes

The Battle of the Sexes describes asymmetric conflicts in mating behavior of males and females. Males can be philanderer or faithful, while females are either fast or coy, leading to a cyclic dynamics. The adjusted replicator equation predicts stable coexistence of all four strategies. In this situation, we consider the effects of fluctuations stemming from a finite population size. We show that they unavoidably lead to extinction of two strategies in the population. However, the typical time until extinction occurs strongly prolongs with increasing system size. In the meantime, a quasi-stationary probability distribution forms that is anomalously flat in the vicinity of the coexistence state. This behavior originates in a vanishing linear deterministic drift near the fixed point. We provide numerical data as well as an analytical approach to the mean extinction time and the quasi-stationary probability distribution.

The time-delay effect of a metapopulation

The simplified incidence function model with small delay time was employed to study the stability and mean extinction time of a metapopulation. By numerically computing the mean passage time and analyzing the stationary probability distribution function of the metapopulation，we found that：1) As delay time increases，the probability that pathe are occupied by a metapopulation decreases; 2) As delay time increases，the mean extinction time of a metapopulation decreases.

Pine Forest Height Inversion Using Single-Pass X-Band PolInSAR Data

A sparse pine forest is investigated at X-band on a single-pass polarimetric synthetic aperture radar interferometry (PolInSAR) data set using HH and HV channels. These first preliminary results show that the associated phase centers present a significant vertical separation (about 6 m) allowed by penetration through gaps in the canopy. Forest parameter inversion using the random volume over ground (RVoG) model is evaluated and adapted at this frequency. The forest height can be retrieved accurately by supposing a high mean extinction coefficient (around 1.6 (dB/m). The penetration depth is estimated to be around 4 m, based on the forest height ground measurements. Finally, a time-frequency analysis using a sublook decomposition is performed to increase the vertical separation of the polarimetric phase centers. As a consequence, RVoG-inversion performance is improved, and a penetration depth that is in better accordance with a previous work (of the order of 2 m) is found. This paper has shown that the height inversion of a pine forest was possible using PolInSAR X-band data and that the performance was more dependent on the forest density than at lower frequencies.

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Abstract. Optical and geometrical characteristics of cirrus clouds over Thessaloniki, Greece (40.6° N, 22.9° E) have been determined from the analysis of lidar and radiosonde measurements performed during the period from 2000 to 2006. Cirrus clouds are generally observed in a mid-altitude region ranging from 8.6 to 13 km, with mid-cloud temperatures in the range from −65° to −38°C. The cloud thickness generally ranges from 1 to 5 km and 38{%} of the cases studied have thickness between 2 and 3 km. The retrieval of optical depth and lidar ratio of cirrus clouds is performed using three different methods, taking into account multiple scattering effect. The mean optical depth is found to be 0.31±0.24 and the corresponding mean lidar ratio is 30±17 sr following the scheme of Klett-Fernald method. Sub-visual, thin and opaque cirrus clouds are observed at 3%, 57% and 40% of the measured cases, respectively. A comparison of the results obtained between the three methods shows good agreement. The multiple scattering errors of the measured effective extinction coefficients range from 20 to 60%, depending on cloud optical depth. The temperature and thickness dependencies on optical properties have also been studied in detail. A maximum mid-cloud depth of ~3.5 km is found at temperatures around ~−47.5°C, while there is an indication that optical depth and mean extinction coefficient increases with increasing mid-cloud temperature. A correlation between optical depth and thickness was also found. However, no clear dependence of the lidar ratio values on the cloud temperature and thickness was found.

Probabilistic approach in weighted Markov branching processes

This note provides a new probabilistic approach in discussing the weighted Markov branching process (WMBP) which is a natural generalisation of the ordinary Markov branching process. Using this approach, some important characteristics regarding the hitting times of such processes can be easily obtained. In particular, the closed forms for the mean extinction time and conditional mean extinction time are presented. The explosion behaviour of the process is investigated and the mean explosion time is derived. The mean global holding time and the mean total survival time are also obtained. The close link between these newly developed processes and the well-known compound Poisson processes is investigated. It is revealed that any weighted Markov branching process (WMBP) is a random time change of a compound Poisson process.

An iterative calculation to derive extinction-to-backscatter ratio based on lidar measurements

The aerosol optical thickness (AOT) is an important parameter for understanding the radiative impact of aerosols. AOT based on lidar measurements is often limited by its finite detection range. In this paper, we have reported a method of fitting and iterative calculation to derive the extinction profile of background aerosols from 0 to 30 km at 532 nm, which is virtually the AOT of the entire atmosphere. The mean extinction derived from this method at the ground level tallies with visibility measurement and it is also consistent with the sun-photometer data, within experimental error. These data have been further treated to study the dust cases. For most of the cases, transmission losses were determined to estimate the extinction as well as lidar ratio. The result of the analysis shows that for background aerosols, a mean lidar ratio of 47±15 sr was found. For dust layers, a mean lidar ratio of 44±19 sr and an optical thickness of 0.53±0.49 were determined at 532 nm.

Experimental and theoretical studies on high-temperature thermal properties of fibrous insulation

In the present paper, an experimental apparatus has been developed to measure heat transfer through high-alumina fibrous insulation for thermal protection system. Effective thermal conductivities of the fibrous insulation were measured over a wide range of temperature (300–973 K) and pressure (10 −2–10 5 Pa) using the developed apparatus. The specific heat and the transmittance spectra in the wavelength range of 2.5–25 μm were also measured. The spectral extinction coefficients and Rosseland mean extinction coefficients were obtained from transmittance data at various temperatures to investigate the radiative heat transfer in fibrous insulation. A one-dimensional finite volume numerical model combined radiation and conduction heat transfer was developed to predict the behavior of the effective thermal conductivity of the fibrous insulation at various temperatures and pressures. The two-flux approximation was used to model the radiation heat transfer through the insulation. The experimentally measured specific heat and Rosseland mean extinction coefficients were used in the numerical heat transfer model to calculate the effective thermal conductivity. The average deviation between the numerical results for different values of albedo of scattering and the experimental results was investigated. The numerical results for ω=1 and experimental data were compared. It was found that the calculated values corresponded with the experimental values within an average of 13.5 percent. Numerical results were consistent with experimental results through the environmental conditions under examination.

Measurement of radiative thermal properties of thin polymer films by FTIR

Although a number of test methods have been reported for the characterization of radiative thermal properties of semi-transparent materials and textile fabrics, the need for specialized equipment limited the application of these test methods. This paper reports on the use of a conventional instrument, viz. Fourier transform infrared (FTIR) spectroscopy, for the characterization of radiative thermal properties of thin polymer films for application within an intermediate temperature range. Experimental measurements on spectral transmission with FTIR were performed on four types of thin films with high mass fraction, viz. one made of polyethylene (PE), two made of polyamide (NB and NW) and one made of aluminium foil (AF). From the measurements, extinction coefficients were calculated by using Beer's Law, and then the Rosseland mean extinction coefficients and radiative thermal conductivities were determined. The results showed that the thin AF film was the best at blocking radiation, whereas the thin PE film was the weakest. The two polyamide films (NB and NW), made of the same polymer but different in colour, had similar intermediate capability in blocking radiation, indicating colour has little effect on radiative thermal properties of polymeric materials.

Cirrus optical properties observed with lidar, radiosonde, and satellite over the tropical Indian Ocean during the aerosol‐polluted northeast and clean maritime southwest monsoon

Cirrus formation and geometrical and optical properties of tropical cirrus as a function of height and temperature are studied on the basis of INDOEX (Indian Ocean Experiment) lidar and radiosonde measurements and satellite observations of deep convection causing the generation of anvil cirrus. Lidar and radiosonde measurements were conducted at Hulule (4.1°N, 73.3°E), Maldives, during four field campaigns carried out in February–March 1999 and March 2000 (northeast (NE) monsoon season, characterized by increased concentrations of anthropogenic aerosols over the Indian Ocean) and in July and October 1999 (southwest (SW) monsoon season, characterized by clean maritime conditions). As a result of a stronger impact of deep convection on cirrus formation during the SW monsoon season, cirrus clouds covered the sky over the lidar site in only 35% (NE), but 64% (SW) of the measurement time. Subvisible cirrus (optical depth ≤0.03), thin (optical depth from 0.03 to 0.3), and opaque cirrus (optical depth ≥0.3) were observed in 18%, 48%, and 34% (NE) and in 8%, 52%, and 40% (SW) out of all cirrus cases, respectively. Mean midcloud heights were rather similar with values of 12.9 ± 1.5 km (NE) and 12.7 ± 1.3 km (SW). In 25% of the cases the cirrus top height was found close to the tropopause. Mean values of the multiple‐scattering‐corrected cirrus optical depth, cirrus layer mean extinction coefficient, and extinction‐to‐backscatter ratio were 0.25 ± 0.26 (NE) and 0.34 ± 0.29 (SW), 0.12 ± 0.09 km−1 (NE) and 0.12 ± 0.10 km−1 (SW), and 33 ± 9 sr (NE) and 29 ± 11 sr (SW), respectively. A functional dependency of the extinction coefficient of the tropical cirrus on temperature is presented. All findings are compared with several other cirrus lidar observations in the tropics, subtropics, and at midlatitudes. By contrasting the cirrus optical properties of the different seasons, a potential impact of anthropogenic particles on anvil cirrus optical properties was examined. Differences in the cirrus extinction‐to‐backscatter ratio suggest that NE monsoon anvil cirrus originating from deep‐convection cumulus clouds had more irregularly shaped and thus slightly larger ice crystals than respective SW monsoon anvil cirrus. Because the meteorological conditions were found to vary significantly between the seasons, an unambiguous identification of the influence of Asian haze on cirrus optical properties is not possible.

Optical and Near‐IR Imaging of the Dark Globule CB 52

The internal structure of the dark globule CB 52 is investigated by means of broadband imaging in the optical and near-IR spectral range. By exploiting the extinction of the stellar light within this object, we derive observational parameters suitable to infer the internal structure of this cloud. Extinction maps were obtained at different wavelengths by using both stellar counts and two-color diagrams. While in the optical region the extinction is better evaluated at the cloud boundaries, the internal regions are more conveniently probed in the near-IR, so a combined map was derived. The total-to-selective extinction ratio RV was also observed to increase toward the inner regions, and a plot versus the extinction AV suggests that grain growth processes are active in this cloud. The statistical fluctuation of the AV, estimated in the line of sight of the background stars, is investigated by comparing the observed stellar colors with those of the unreddened stars. The dispersion σAV, derived from optical observations, is found to be almost independent of the mean extinction, AV, while by using near-IR data we find a more complex behavior: the σAV versus AV relation increases until AV ~ 6 and then decreases for larger extinctions. This is discussed in the framework of a simple model, suggesting that a clumpy and clustered structure can explain the observations in the inner regions, while outside the cloud the mass distribution remains more homogeneous.

Improved Distances to Type Ia Supernovae with Multicolor Light‐Curve Shapes: MLCS2k2

We present an updated version of the multicolor light-curve shape method to measure distances to Type Ia supernovae (SNe Ia), incorporating new procedures for K-correction and extinction corrections. We also develop a simple model to disentangle intrinsic color variations and reddening by dust and expand the method to incorporate U-band light curves and to more easily accommodate prior constraints on any of the model parameters. We apply this method to 133 nearby SNe Ia, including 95 objects in the Hubble flow (cz ≥ 2500 km s-1), which give an intrinsic dispersion of less than 7% in distance. The Hubble flow sample, which is of critical importance to all cosmological uses of SNe Ia, is the largest ever presented with homogeneous distances. We find that the Hubble flow SNe with H0dSN ≥ 7400 km s-1 yield an expansion rate that is 6.5% ± 1.8% lower than the rate determined from SNe within that distance, and this can have a large effect on measurements of the dark energy equation of state with SNe Ia. Peculiar velocities of SN Ia host galaxies in the rest frame of the Local Group are consistent with the dipole measured in the cosmic microwave background. Direct fits of SNe Ia that are significantly reddened by dust in their host galaxies suggest that their mean extinction law may be described by RV 2.7, but optical colors alone provide weak constraints on RV.

Evaluation of Ecotoxicity Effect Indicators for Use in LCIA (10+4 pp)

Goal, Scope and Background The paper describes different ecotoxicity effect indicator methods/approaches. The approaches cover three main groups, viz. PNEC approaches, PAF approaches and damage approaches. Ecotoxicity effect indicators used in life cycle impact assessment (LCIA) are typically modelled to the level of impact, indicating the potential impact on 'ecosystem health'. The few existing indicators, which are modelled all the way to damage, are poorly developed, and even though relevant alternatives from risk assessment exist (e.g. recovery time and mean extinction time), these are unfortunately at a very early stage of development, and only few attempts have been made to include them in LCIA.

Dust Absorption Along the Line of Sight for High‐Redshift Objects

We estimate the optical depth distribution of dust present in absorption systems along the line of sight of high-redshift galaxies and the resulting reddening. We characterize the probability distribution of the transmission to a given redshift and the shape of the effective mean extinction law by means of analytical estimates and Monte Carlo simulations. We present our results in a format useful for applications to present samples of high-redshift galaxies and discuss the implications for observations with the James Webb Space Telescope. Our most realistic model takes into account the metallicity evolution of damped Lyα absorbers and predicts that the effects of dust absorption are modest: at redshift z 5 the transmission is above 0.8 at an emitted wavelength λe = 0.14 μm with probability 90%. Therefore, dust obscuration along the line of sight will affect only marginally observations at very high redshift.