From the help desk: Transfer functions

The question often arises as to whether one can estimate a transfer function model using Stata. While Stata does not currently have a convenience command for doing so, this article will demonstrate that estimating such a model can be accomplished quite easily using Stata's arima command. The classic text for transfer function modeling is Box, Jenkins, and Reinsel (1994); however, a more concise presentation can be found in Brockwell and Davis (1991). Copyright 2002 by Stata Corporation.arima, xcorr, corrgram, transfer function, impulse-response function, autocorrelation function, cross-correlation function, pre-whitened, linear filter, difference equation

From the help desk: Polynomial distributed lag models

Polynomial distributed lag models (PDLs) are finite-order distributed lag models with the impulse-response function constrained to lie on a polynomial of known degree. You can estimate the parameters of a PDL directly via constrained ordinary least squares, or you can derive a reduced form of the model via a linear transformation of the structural model, estimate the reduced-form parameters, and recover estimates of the structural parameters via an inverse linear transformation of the reduced-form parameter estimates. This article demonstrates both methods using Stata. Copyright 2004 by StataCorp LP.polynomial distributed lag, Almon, Lagrangian interpolation polynomials

From the help desk

Welcome to From the help desk. From the help desk is written by the people in Technical Services at StataCorp and deals with issues that they have found to be of concern to a large fraction of Stata users. It is the rare column in this series that deals with sophisticated programming issues because such issues, by definition, are not of concern to a large fraction of Stata users. From the help desk discusses the use of sophisticated programs and the use of sophisticated statistics. Copyright 2001 by Stata Corporation.internet, web, ado-files, Stata executable installation, updates, downloading, user-written additions, packages, search, find

From the help desk: It's all about the sampling

Effective estimation and inference, when the data are collected using complex survey designs, requires estimators that fully account for the sampling design. This article explores, by means of Monte Carlo simulations of the power of simple hypothesis tests, the consequences of parameter estimation and inference when naive estimators are employed with survey data. Copyright 2002 by Stata Corporation.cluster, design, power, strata, svy, svymean, svyset

An evaluation of quartz-inclusion barometry by laser Raman microspectrometry : a case study from the Llano Uplift of central Texas

textA new barometric technique measuring stored stress in quartz inclusions via laser Raman microspectrometry was employed in an attempt to elucidate the extent of highpressure (HP) metamorphism in the Llano Uplift of central Texas. Rare lithologies within the Llano Uplift contain mineralogical evidence of HP metamorphism (pressures from 1.4 to 2.4 GPa at temperatures from 650 to 775°C), but much of the uplift is composed of felsic gneisses lacking any HP signature; these felsic gneisses may never have transformed to HP assemblages, or they may have been thoroughly overprinted by later low-pressure events. Barometry via laser Raman microspectrometry computes entrapment pressure for a quartz inclusion in garnet from measurement of the displacements of its Raman peak positions from those of a quartz standard at atmospheric pressure. Quartz inclusions in garnets that grew in felsic gneisses under HP conditions should retain HP signatures, despite later overprinting. Application of the Raman microspectrometry technique should therefore allow barometry of previously uncharacterizable rocks. For two localities in the Llano Uplift, entrapment pressures from Raman barometry (0.6-0.7 GPa and 0.2-0.3 GPa) were substantially lower than pressures expected based on conventional barometers (1.4 GPa and 1.6-2.4 GPa). This absence of any HP signatures in the Llano rocks contrasts with more successful applications of the Raman technique by previous workers in high P/T blueschist-facies rocks. A key difference in the Llano rocks is that they reached peak temperatures at which intracrystalline diffusion in garnet, driven by compositional gradients produced during growth, had noticeable effects: complete homogenization of growth zoning had occurred in the locality that produced the greatest discrepancies between Raman and conventional pressures, and modest relaxation of zoning occurred in the locality with the smaller discrepancies. The failure of the Raman technique to recover pressures consistent with conventional barometry in the Llano Uplift is therefore attributed to relaxation of stress on the quartz inclusions as the result of intracrystalline diffusion within the garnet. This conclusion suggests that use of the Raman barometric technique must be restricted to rocks whose time-temperature histories produce only very limited intracrystalline diffusion in garnet, typically those rocks whose peak metamorphic temperatures fall at or below upper amphibolite-facies conditions.Geological Science

An Ecohydrological Perspective on Drought-induced Forest Mortality

Regional‐scale drought‐induced forest mortality events are projected to become more frequent under future climates due to changes in rainfall patterns. The occurrence of these mortality events is driven by exogenous factors such as frequency and severity of drought and endogenous factors such as tree water and carbon use strategies. To explore the link between these exogenous and endogenous factors underlying forest mortality, a stochastic ecohydrological framework that accounts for random arrival and length of droughts as well as responses of tree water and carbon balance to soil water deficit is proposed. The main dynamics of this system are characterized with respect to the spectrum of anisohydric‐isohydric stomatal control strategies. Using results from a controlled drought experiment, a maximum tolerable drought length at the point where carbon starvation and hydraulic failure occur simultaneously is predicted, supporting the notion of coordinated hydraulic function and metabolism. We find qualitative agreement between the model predictions and observed regional‐scale canopy dieback across a precipitation gradient during the 2002–2003 southwestern United States drought. Both the model and data suggest a rapid increase of mortality frequency below a precipitation threshold. The model also provides estimates of mortality frequency for given plant drought strategies and climate regimes. The proposed ecohydrological approach can be expanded to estimate the effect of anticipated climate change on drought‐induced forest mortality and associated consequences for the water and carbon balances

IVOA Recommendation: IVOA Photometry Data Model

The Photometry Data Model (PhotDM) standard describes photometry filters, photometric systems, magnitude systems, zero points and its interrelation with the other IVOA data models through a simple data model. Particular attention is given necessarily to optical photometry where specifications of magnitude systems and photometric zero points are required to convert photometric measurements into physical flux density units

Climate change impacts and adaptation to permafrost change in High Mountain Asia: a comprehensive review

Changing climatic conditions in High Mountain Asia (HMA), especially regional warming and changing precipitation patterns, have led to notable effects on mountain permafrost. Comprehensive knowledge of mountain permafrost in HMA is mostly limited to the mountains of the Qinghai-Tibetan Plateau, with a strong cluster of research activity related to critical infrastructure providing a basis for related climate adaptation measures. Insights related to the extent and changing characteristics of permafrost in the Hindu Kush Himalaya (HKH), are much more limited. This study provides the first comprehensive review of peer-reviewed journal articles, focused on hydrological, ecological, and geomorphic impacts associated with thawing permafrost in HMA, as well as those examining adaptations to changes in mountain permafrost. Studies reveal a clear warming trend across the region, likely resulting in increased landslide activity, effects on streamflow, soil saturation and subsequent vegetation change. Adaptation strategies have been documented only around infrastructure megaprojects as well as animal herding in China. While available research provides important insight that can inform planning in the region, we also identify a need for further research in the areas of hazards related to changing permafrost as well as its effect on ecosystems and subsequently livelihoods. We suggest that future planning of infrastructure in HMA can rely on extrapolation of already existing knowledge within the region to reduce risks associated with warming permafrost. We highlight key research gaps as well as specific areas where insights are limited. These are areas where additional support from governments and funders is urgently needed to enhance regional collaboration to sufficiently understand and effectively respond to permafrost change in the HKH region

Ecosystem thresholds, tipping points, and critical transitions

An organized session at the American Geophysical Union Fall Meeting in New Orleans, Louisiana, USA, December 201