bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal association of onset of daily smoking with adolescent substance use and psychiatric morbidity
Authors: Ilomäki Risto , Riala Kaisa , Hakko Helinä , Lappalainen Jaakko , Ollinen Taru , Räsänen Pirkko , Timonen Markku
Published: December 2007

Objective

The association between cigarette smoking and psychiatric disorders is well established for adult populations. However, only limited number of studies has investigated whether the young onset age of daily smoking (DS) among adolescents is associated with psychiatric morbidity and vice versa.

Methods

Data from 508 adolescents admitted to psychiatric hospitalization were collected. Cox proportional hazard model were used to compare the initiation of DS between adolescents with and without substance use (SUD), and other psychiatric disorders.

Results

Rates of DS were high in each diagnostic category. Boys started smoking at younger age (mean 12.4 years) than girls (13.0 years). Both boys and girls diagnosed with conduct or oppositional defiant disorders (COD) and also girls with SUD started daily smoking earlier as compared to those of same gender without these disorders.COD were found to be primary to the initiation of DS among boys. SUD, psychotic, and depressive disorders (DEP) were found to be secondary to DS among both genders.

Conclusions

DS in adolescence is related with later SUD. COD are associated with subsequent initiation of DS among boys. The temporal gap between smoking initiation and COD is shorter among girls. Gender difference plays a role in association of DS and DEP. Initiation of DS at very early age should alert health care professionals of development of later psychopathology, especially SUD.
Dementia: Is it time for a change in focus?
Authors: Kuller Lewis H. , Lopez Oscar L.
Published: December 2007

One of Dr Leon Thal's major contributions to Alzheimer's disease (AD) research was the network of clinical trials and his strong commitment to finding effective therapies for both the prevention and treatment of AD in the population. AD and dementia research has matured since the inception of the Alzheimer's Disease Center program from a primary social service problem to clinical‐pathologic correlates and better definition of disease to evaluation of measures of cognition, in vivo images of the brain, and then to measures of beta amyloid and tau in vivo and relationship to clinical dementia. Unfortunately, we still do not know the etiology of AD or the relationship to other brain abnormalities such as vascular disease and Lewy bodies. We also do not have good preventive or treatment strategies. Both are badly needed. The critical question is whether this field is ready for a major change in focus from primarily a descriptive science to analytical, longitudinal studies testing new research hypotheses that will lead to better preventive and treatment approaches.
Psychosocial determinants of intention to screen for Alzheimer's disease
Authors: Galvin James E. , Fu Qiang , Nguyen Joseph T. , Glasheen Cristie , Scharff Darcell P.
Published: December 2007

Background

There is little information about how receptive older adults are to discuss memory problems with healthcare providers. Here we test the psychosocial factors explaining older adults' intention to undergo screening for Alzheimer disease (AD).

Methods

A population‐based, random‐digit dialing strategy surveyed 1,039 older adults. The Behavioral Model of Health Services Use was used as a conceptual framework for a questionnaire testing constructs from several behavioral theories. Structural equation modeling assessed the relationship of latent variables to each construct with goodness‐of‐fit indices.

Results

The study had an 82% response rate and 72% completer rate. The respondents' mean age was 62.7 ± 10.2 years (range, 50 to 97 years). The sample was 67% women, 86% were white, and less than 40% had personal experience with AD. Respondents were nondemented (Short Blessed scores, 1.7 ± 2.2). Predictors of intention to screen included perceived benefits (γ = .35), knowledge of dementia (γ = .26), self‐efficacy (γ = .23), preventive health behaviors (γ = .17), and perceived susceptibility (γ = .14). Knowledge was positively correlated with perceived benefits (φ = .29) and susceptibility (φ = .20). Preventive behaviors (φ = .20) were positively correlated with perceived benefits. Self‐efficacy correlated positively with preventive behaviors (φ = .24) and perceived benefits (φ = .37) and negatively with perceived susceptibility (φ = −.11). Goodness‐of‐fit indices suggested a good fit of this model (root mean square error of approximation, .037; comparative fit index, 0.98; relative fit index; .96).

Discussion

Older adults who have knowledge of dementia and perceive benefit from diagnosis and treatment are more likely to exhibit willingness and confidence to be tested for cognitive problems. Individuals with high self‐efficacy, perceived susceptibility, and positive preventive health behaviors are also more likely to exhibit intention. These constructs can now be used to develop interventions to evaluate cognitive health in the elderly.
Exploring human/animal intersections: Converging lines of evidence in comparative models of aging
Authors: Trojanowski John Q. , Hendricks Joan C. , Jedrziewski Kathryn , Johnson F. Brad , Michel Kathryn E. , Hess Rebecka S. , Cancro Michael P. , Sleeper Meg M. , Pignolo Robert , Teff Karen L. , Aguirre Gustavo D. , Lee Virginia M.-Y. , Lawler Dennis F. , Pack Allan I. , Davies Peter F.
Published: December 2007

At a symposium convened on March 8, 2007 by the Institute on Aging at the University of Pennsylvania, researchers from the University's Schools of Medicine and Veterinary Medicine explored the convergence of aging research emerging from the two schools. Studies in human patients, animal models, and companion animals have revealed different but complementary aspects of the aging process, ranging from fundamental biologic aspects of aging to the treatment of age‐related diseases, both experimentally and in clinical practice. Participants concluded that neither animal nor human research alone will provide answers to most questions about the aging process. Instead, an optimal translational research model supports a bidirectional flow of information from animal models to clinical research.
Home‐based technologies: A new paradigm for conducting dementia prevention trials
Authors: Kaye Jeffrey
Published: December 2007

The approach toward treatment of Alzheimer's disease has evolved out of a large body of research, resulting in a common trial paradigm directed toward establishing efficacy and safety of putative treatments for dementia. To achieve the ultimate goal of preventing dementia, the future will build on this model but will need to incorporate new paradigms to more efficiently detect meaningful change over time. Among new innovations needed is the capability for assessing trajectories of change over many years. Intrinsic to this success is the ability to capture increasing variability as well as subject heterogeneity inherent in longitudinal aging cohorts. New methods of ubiquitous embedded home sensing and computing afford the opportunity to assess volunteers not only during long periods of time but with greater frequency and convenience. Clinical studies identifying the optimal ways of using these methods are needed.
Oral administration of circulating precursors for membrane phosphatides can promote the synthesis of new brain synapses
Authors: Cansev Mehmet , Wurtman Richard J. , Sakamoto Toshimasa , Ulus Ismail H.
Published: December 2007

Although cognitive performance in humans and experimental animals can be improved by administering omega‐3 fatty acid docosahexaenoic acid (DHA), the neurochemical mechanisms underlying this effect remain uncertain. In general, nutrients or drugs that modify brain function or behavior do so by affecting synaptic transmission, usually by changing the quantities of particular neurotransmitters present within synaptic clefts or by acting directly on neurotransmitter receptors or signal‐transduction molecules. We find that DHA also affects synaptic transmission in mammalian brain. Brain cells of gerbils or rats receiving this fatty acid manifest increased levels of phosphatides and of specific presynaptic or postsynaptic proteins. They also exhibit increased numbers of dendritic spines on postsynaptic neurons. These actions are markedly enhanced in animals that have also received the other two circulating precursors for phosphatidylcholine, uridine (which gives rise to brain uridine diphosphate and cytidine triphosphate) and choline (which gives rise to phosphocholine). The actions of DHA aere reproduced by eicosapentaenoic acid, another omega‐3 compound, but not by omega‐6 fatty acid arachidonic acid. Administration of circulating phosphatide precursors can also increase neurotransmitter release (acetylcholine, dopamine) and affect animal behavior. Conceivably, this treatment might have use in patients with the synaptic loss that characterizes Alzheimer's disease or other neurodegenerative diseases or occurs after stroke or brain injury.
Chronic disease long‐term drug prevention trials: Lessons from the Alzheimer's Disease Anti‐inflammatory Prevention Trial (ADAPT)
Authors: Meinert Curtis L. , Breitner John C.S.
Published: December 2007

A randomized trial is a randomized trial. The basic ingredients do not change with different purposes whether for treatment or prevention of disease. Likewise, the problems and difficulties are mostly the same. But there are differences in approach and philosophy. Here we discuss problems in trials focused on healthy people to determine whether drugs can delay or prevent adverse health events, with the Alzheimer's Disease Anti‐inflammatory Prevention Trial (ADAPT) as an example. An important difference separating treatment trials from prevention trials is the length of time needed to demonstrate a difference with treatment. Related to this is the risk‐benefit calculus of the trial. Treatment trials are aimed at “curing” or ameliorating disease, for example, as with trials involving people with Alzheimer's disease (AD) dementia to determine whether treatment is useful in dealing with the AD‐induced dementia. Like other treatment trials, those targeting AD dementia balance these benefits against the risks of treatment. But by contrast, benefit in prevention trials, if any, will be found only in the absence or delay in disease onset, often after years of continuous treatment. As in ADAPT, the separation in timing of risk versus benefit often brings difficult decisions about how long to continue the trial in the absence of any apparent benefit to treatment. Other difficulties similarly relate to the length of prevention trials. In hopes that some lessons learned from ADAPT will assist future prevention trials, especially in the elderly, we describe several conundrums and problems experienced in this trial and attempt when possible to extend our observations to the larger class of long‐term drug prevention trials.
More than a decade of estrogen neuroprotection
Authors: Simpkins James W. , Singh Meharvan
Published: December 2007

Considerable evidence has emerged through more than a decade of research supporting the neuroprotective and cognition‐preserving effects of estrogens. Such basic research coupled with various epidemiological studies led quickly to the assessment of Premarin for the treatment of mild to moderate Alzheimer's disease (AD), initiated by the Alzheimer's Disease Cooperative Study Group and headed by Dr. Leon Thal. While this and subsequent trials with Premarin (Wyeth Research, Monmouth Junction, New Jersey) and PremPro (Wyeth Research), a conjugated equine estrogen preparation plus medoxyprogresterone acetate, have not supported the use of estrogens in treating advanced AD, considerable inferences have been made from these placebo controlled trials of estrogens. Here, we aimed to put these AD trials of estrogens in perspective by considering the potential mechanisms of these potent neuroprotective estrogens, the role of estrogens in other neurodegenerative conditions, such as cerebral ischemia, and based on our current understanding of estrogen neurobiology, offer insight into the design of future clinical trails of estrogens for neuronal protection.
We should not distinguish between symptomatic and disease‐modifying treatments in Alzheimer's disease drug development
Authors: Doody Rachelle S.
Published: December 2007

The terms symptomatic and disease‐modifying have become standard in discussions of Alzheimer's disease therapeutics, yet there is little justification for their use. Currently marketed drugs are presumed to be symptomatic because they lead to some degree of mean improvement over baseline and because of the widespread belief that their mechanisms are limited and their effects are completely reversible. Current trial methodologies cannot distinguish between symptomatic and disease‐modifying effects. Furthermore, it is highly likely that many trials will demonstrate a combination of such effects at the level of the trial or at the level of the individual. The forces that drive this distinction are largely social, as opposed to scientific. It would be preferable for drugs to first seek an antidementia claim, preferably on the background of conventional therapies when possible, in trials that are as small and as short in duration as possible. Further refinements would come by demonstration of how substantial and how enduring the antidementia benefits are.
Challenges to the recognition and assessment of Alzheimer's disease in American Indians of the southwestern United States
Authors: Griffin‐Pierce Trudy , Silverberg Nina , Connor Donald , Jim Minnie , Peters Jill , Kaszniak Alfred , Sabbagh Marwan N.
Published: December 2007

Little is known about Alzheimer's disease (AD) and related neurodegenerative diseases in American Indian (AI) populations. To provide appropriate health care to elder AIs, whose population is expected to increase dramatically during the next 50 years, it is imperative to attain a better understanding of the interaction of culture and disease in this underserved population. Raising awareness in the AI population regarding the nature of dementia as it compares to normal aging and the development of culturally appropriate instruments to detect and stage AD are essential for future health care efforts. Barriers restricting clinical service to this population include historical factors relating to access to health care, cultural beliefs regarding aging, demographic diversity of the population, competing epidemiologic risk factors, and lack of proper assessment tools for clinicians.
Commentary on “Perspective on race and ethnicity in Alzheimer's disease research”
Authors: Griffith Derek M. , Griffith Patrick A.
Published: December 2007

There are persistent disparities in Alzheimer's disease by race and ethnicity that are not well understood. The emphasis given to seeking a genetic basis for racial differences might be a distraction from the more relevant issue of identifying preventable causes of Alzheimer's disease. The majority of Alzheimer's disease cases are diagnosed as the late onset type and are unlikely to be inherited. Late onset Alzheimer's disease cases, therefore, more likely represent variations in gene expression than gene frequency. Although conceptual and methodologic problems have limited our understanding of this relationship, race‐based studies provide important opportunities to understand the environmental factors associated with gene expression. Improving our understanding of the factors associated with race and ethnicity might help to clarify the epidemiology and course of Alzheimer's disease.
Perspective on race and ethnicity in Alzheimer's disease research
Authors: Weiner Myron F.
Published: December 2007

There are adequate scientific, public health, and ethical justifications for studying Alzheimer's disease (AD) in persons of varying race and ethnicity, but to be meaningful variables, race and ethnicity must be examined in context. The complex interactions between race, ethnicity, lifestyle, and environmental factors, such as climate and diet, require that future studies of AD in specific racial or ethnic groups attend to measures of racial/ethnic homogeneity and the assessment of the environment and the elements that comprise the ethnicity of groups under study. Instead of arbitrarily selecting specific racial or ethnic groups in the hope of finding important differences, it may be in the long run less costly and more efficient to recruit families with highly positive (or negative) family histories, to search within these groups for possible racial or ethnic differences, and to investigate the possible racial or ethnic reasons for those differences.
Drug discovery and the prevention of Alzheimer's disease
Authors: Fillit Howard
Published: December 2007

Progress in understanding the pathogenesis of Alzheimer's disease (AD) has advanced rapidly and has achieved parity in knowledge with other chronic degenerative diseases of the elderly. This knowledge has not yet been successfully translated into new and effective disease‐modifying drugs. Many new clinical candidates are currently in clinical trials, and it is likely that some will be successful in achieving regulatory approval. Nevertheless, primary prevention of AD remains the ultimate and most important goal of research efforts because the unique clinical features of this dementing disease create a number of challenges for drug development, regulatory approval, and payment. Ultimately, the development of truly effective disease‐modifying drugs through accelerated drug discovery is the only real pathway to primary prevention.
Current and future management of Alzheimer's disease
Authors: Gauthier Serge , Poirier Judes
Published: December 2007

The full span of Alzheimer's disease, from asymptomatic, pre‐dementia, mild‐to‐moderate stages, should be considered in the management. There are multiple research opportunities for better understanding and treatment of this condition. Ongoing cohort studies developed under Leon Thal's leadership will facilitate this process.
A perspective on risks that impede development of drugs to modify the course of Alzheimer's disease: Can they be reduced?
Authors: Mohs Richard C.
Published: December 2007

Discovery, development, and testing of new drugs with novel mechanisms and new indications are extremely risky. The number of new drugs introduced into clinical practice with new mechanisms and novel indications has not increased during recent years in spite of advances in biologic science. The sources of uncertainty leading to failure in drug development are discussed in three categories: biologic or target risk, clinical development uncertainty, and market uncertainty. Efforts to develop drugs that modify the course of Alzheimer's disease and/or delay the initial clinical manifestations of disease are subject to all three types of risk. Opportunities for government, academic researchers, advocacy groups, and the pharmaceutical industry to mitigate some of these risks and possibly speed the introduction of new therapies are mentioned.
Oncocytoma in the mandibular salivary gland of a cat
Authors: Brocks Bouvien A. , Peeters Marijke E. , Kimpfler Simon
Published: December 2007

A cat was referred for investigation of a soft tissue mass caudal to the left mandible. Initial investigations suggested a malignant salivary gland tumour, and the mass was removed by extracapsular resection of the mandibular gland. Histopathology showed an oncocytoma within the salivary gland. An oncocytoma is a neoplastic transformation of oncocytes. Oncocytes are cells with a small nucleus and intense eosinophilic granular cytoplasm due to numerous mitochondria, which proliferate during ageing in exocrine and endocrine glandular tissues. Physiological proliferation occurs next to oncocytosis, oncocytoma, and oncocytic carcinoma. This is the first report of an oncocytoma in a feline mandibular salivary gland, and the first report of long-term survival after surgical removal.
Gastric dilatation–volvulus associated with diaphragmatic hernia in three cats: Clinical presentation, surgical treatment and presumptive aetiology
Authors: Formaggini Luca , Schmidt Karin , De Lorenzi Davide
Published: December 2007

Three cats were examined because of acute dyspnoea and sudden abdominal enlargement. In all cats, radiographs revealed gastric dilatation–volvulus (GDV) and diaphragmatic hernia. Cardiovascular shock and dyspnoea were treated by intravenous fluid-therapy, oxygen administration and relief of diaphragmatic pressure by means of stomach decompression and in one case placing the patient in an inclined position. Gastric decompression was performed by needle gastrocentesis, placement of a rhino-gastric tube, or a combination of these. Diaphragmatic herniorrhaphy was performed in either case; one cat also underwent gastropexy. The immediate postoperative period resolved uneventfully and the cats were doing well at follow-up. Feline GDV is a rare event in which diaphragmatic hernia may be a predisposing factor.
Mayanian (1100–850 Ma) – Prebaikalian Upper Riphean of Siberia
Authors: Khomentovsky V.V. , Nagovitsin K.E. , Postnikov A.A.
Published: December 2007

The Mayanian (1100–850 Ma) is an all-Siberian stratigraphic subdivision of the Neoproterozoic distinguished on the basis of generalized geological and paleontological data for the Maya Group in the southeast of the Siberian craton and for its counterparts in other structure-facies areas (SFA). The Mayanian deposits in all principally different structures of every SFA, such as intracratonic depressions, pericratonic troughs, and marginal parts of blocks with oceanic crust, were incorporated into the craton in the Vendian. It is separated from the surrounding stratigraphic divisions, Baikalian and Aimchanian, by distinct tectonic boundaries coinciding in time with the formation and starting breakup of the supercontinent Rodinia, i.e., with global events. In the adjacent parts of the platform they were reflected in erosion and considerable gaps in sedimentation. These events are well-expressed where they occurred under intense contraction or, on the contrary, are veiled where extension was predominant.

The boundary between the Kerpylian and Lakhandinian, subdivisions of the Mayanian, is not bearing on important events and is hardly traceable throughout the region. Therefore, the base of the Kerpylian is preferable to be taken as the lower boundary of the Upper Riphean. There are attempts to establish this boundary, as it is made for the Phanerozoic, from paleontological data in compositionally similar deposits. These attempts, however, fail in matching this boundary with the base of the Lakhandinian. Distinctive transitions in communities of microfossils and stromatolites appear to be linked to the Mayanian-Baikalian and, undoubtedly, Middle Riphean-Aimchanian boundaries. In the Lakhandinian, on the contrary, the changes that appeared in the Kerpylian only tend to continue. Some taxa typical of the Lakhandinian appear as early as the Kerpylian. In the Lakhandinian their amount gradually increases upsection, until the top of this division. Thus, it is reasonable to start the Upper Riphean with the lower boundary of the Mayanian.

All the main subdivisions of the Siberian Neoproterozoic — Mayanian, Baikalian, and Vendian — are linked to the most important stages of development of this vast and structurally heterogeneous territory. Each of the above-mentioned stratons can be divided, according to historico-geological and paleontological data, into two or three independent interregional subdivisions. Thus, the stratigraphic scheme of the Neoproterozoic of Siberia seems to be promising for the general scale of this period of the Late Precambrian.
Early response of continental Asia to Pleistocene climate cycles (retuned orbital chronologies for Baikal, marine, and ice core records)
Authors: Phedorin M.A. , Goldberg E.L.
Published: December 2007

Assuming orbital modulation of Pleistocene climate cycles, we have generated a new time scale for the Asian geochemical limnic record in the BDP-96-2 Baikal and the KDP-01 Hovsgol cores and updated the chronologies for the global marine δ18O and Vostok ice-gas records. The time scales were obtained by orbital tuning with the assumption of arbitrary but time invariable amplitudes and phase lags of the orbital parameters and responses.

The retuned chronologies highlighted the cycles of eccentricity (100 kyr), obliquity (41 kyr), and precession (23 and 19 kyr), but the combined 70- and 30-kyr cycles became less prominent in the continental (Baikal) record though persisted in the global data (Vostok δD). The residual 70- and 30-kyr harmonics more likely result from errors in the untuned chronology for the Baikal record but are rather due to nonlinearity in the climate response.

We investigated the leads and lags of orbital climate signals with a special focus on the 100-kyr cycle. The phases of precession, obliquity, and eccentricity cycles, compared among the records, showed the lead of the continent. The Baikal geochemical signal at the 100-kyr band led the global glacial and greenhouse CH4 responses and was almost synchronous with the earliest responding polar temperature signal. The reported results characterize the continent as a system highly responsive to eccentricity variations but do not contradict alternative hypotheses for the origin of the 100-kyr cycle in the Earth’s climate history.
Effect of local stress on the interface response to dynamic loading in faulted crust
Authors: Astafurov S.V. , Shilko E.V. , Ruzhich V.V. , Psakhie S.G.
Published: December 2007

The effect of local stress on the interface response to dynamic loading in faulted crust has been studied through MCA (movable cell automata) simulation. Knowing the strain response of a fault block boundary to test impacts, one can estimate the proximity of the fault to critical stress that allows an unstable slip. The computing results are consistent with data of field experiments in fault fragments (vibration, water injection, explosions). The reported analysis makes the basis for a new approach to estimating stress and strain in active faults.
8000 yr of black carbon accumulation in a colluvial soil from NW Spain
Authors: Kaal Joeri , Martínez-Cortizas Antonio , Buurman Peter , Boado Felipe Criado
Published: December 2007

Analytical pyrolysis-GC/MS and solid-state13C NMR (nuclear magnetic resonance) were applied to the NaOH-extractable organic matter fraction of a colluvial soil from Galicia (NW Spain) that represents more than 8500 yr of accumulation. While molecular indicators of vegetation change were looked for, it seemed likely that any such signal was disturbed by the intense fire regime of the area. This conclusion was drawn from (1) the presence of three charcoal layers, (2) the high proportion of aryl C in NMR spectra (non-quantitative) and (3) the prevalence of benzenes and polycyclic aromatic hydrocarbons (PAHs) in the chromatograms (38±6% of total identified peak area), also in charcoal-poor samples. If this conclusion is accurate, the area has been subjected to burning episodes for at least 8000 yr. Additionally, the results indicate that biomass burning residues (black carbon; BC) may become NaOH extractable after long periods of degradation in mineral soil. These results add to our knowledge of the long-term fate of BC in soil, which is a potential agent in the global C cycle.
Human impacts on open ocean mercury concentrations
Authors: Sunderland Elsie M. , Mason Robert P.
Published: December 2007

We develop an empirically constrained multicompartment box model for mercury cycling in open ocean regions to investigate changes in concentrations resulting from anthropogenic perturbations of the global mercury cycle. Using Monte Carlo simulations, we explicitly consider the effects of variability in measured parameters on modeled seawater concentrations. Our simulations show that anthropogenic enrichment in all surface (25%) and deep ocean waters (11%) is lower than global atmospheric enrichment (300–500%) and varies considerably among geographic regions, ranging from >60% in parts of the Atlantic and Mediterranean to <1% in the deep Pacific. Model results indicate that open ocean mercury concentrations do not rapidly equilibrate with atmospheric deposition and on average will increase if anthropogenic emissions remain at their present level. We estimate the temporal lag between changes in atmospheric deposition and ocean mercury concentrations will vary from decades in most of the Atlantic up to centuries in parts of the Pacific.
Long‐term decline of South Pole neutron rates
Authors: Bieber J. W. , Clem J. , Desilets D. , Evenson P. , Lal D. , Lopate C. , Pyle R.
Published: December 2007

The count rate recorded by a neutron monitor at South Pole, Antarctica, displays a long‐term decline over the 32‐year span from 1965 to 1997. The neutron rate follows an 11‐year cycle with maxima at times of low solar activity, but the 1997 peak rate was approximately 8% lower than the 1965 peak rate based on 27‐d averages. This change is much larger than that recorded by any other neutron monitor. We suggest that the South Pole monitor, owing to its unique position at both high latitude and high altitude (2820 m), has enhanced sensitivity at ∼1–3 GV relative to a sea level monitor and may be responding to a change in the intensity of primary cosmic rays in this rigidity region. Measurements of cosmic rays made aboard stratospheric balloons and on the IMP‐8 spacecraft support the possibility of a long‐term change in cosmic ray intensity.
Percolation conditions in fractured hard rocks: A numerical approach using the three‐dimensional binary fractal fracture network (3D‐BFFN) model
Authors: Nakaya Shinji , Nakamura Kiminori
Published: December 2007

We numerically investigate fracture connectivity and percolation conditions in fractured hard rocks using a three‐dimensional binary fractal fracture network (3D‐BFFN) model based on three fractal geometric parameters: the fractal dimensions (D2) of the spatial distribution of fractures, the exponent of the power‐law cumulative fracture length distribution (a), and the maximum fracture length (lmax) normalized by the domain length (L), lmax/L. Numerical results clarify that the percolation threshold in 3D‐BFFN models is strongly controlled by fractal geometric parameters and is independent of any anisotropy in the orientations Θ. In addition, when a < 1.8 and lmax/L < 1.0, percolation seldom occurs independently of D2 and Θ. In the current study the analytical solution of percolation probability (P) is presented as a function of the three fractal parameters within the 3D‐BFFN model. Application of the 3D‐BFFN model to seismogenic fractures determined from the earthquake catalogue in an offshore volcanic region between Miyake‐jima Island (MI) and Kozu‐shima Island (KI) off the Izu Peninsula, Japan, suggests that P is mainly affected by the error involved in determining a during actual surveys. Otherwise, P provides a useful index for determining whether a three‐dimensional domain percolates in fracture networks in fractured hard rocks. The basis of this approach is the observation from fracture network connections that domains with P > 0.55 are percolated domains. The zone of percolation within seismogenic fracture networks between MI and KI reveals that the networks formed from seismic‐swarm‐related seismogenic fractures over a 7‐week period related to the intrusion of a dyke, inferred previously from seismicity and deformation data.
Carbon dioxide degassing at Latera caldera (Italy): Evidence of geothermal reservoir and evaluation of its potential energy
Authors: Chiodini G. , Baldini A. , Barberi F. , Carapezza M. L. , Cardellini C. , Frondini F. , Granieri D. , Ranaldi M.
Published: December 2007

In order to test the potentiality of soil CO2 diffuse degassing measurements for the study of underground mass and heat transfer in geothermal systems detailed surveys were performed at Latera caldera, which is an excellent test site, because of the abundant available subsurface data. Over 2500 measurements of soil CO2 flux revealed that endogenous CO2 at Latera caldera concentrates on a NE‐SW band coinciding with a structural high of fractured Mesozoic limestones hosting a water‐dominated high‐enthalpy geothermal reservoir. The total hydrothermal CO2 degassing from the structural high has been evaluated at 350 t d−1 from an area of 3.1 km2. It has been estimated that such a CO2 release would imply a geothermal liquid flux of 263 kg s−1, with a heat release of 239 MW. The chemical and isotopic composition of the gas indicates a provenance from the geothermal reservoir and that CO2 is partly originated by thermal metamorphic decarbonation in the hottest deepest parts of the system and partly has a likely mantle origin. The ratios of CO2, H2, CH4, and CO to Ar were used to estimate the T‐P conditions of the reservoir. Results cluster at T ∼ 200–300°C and PCO2 ∼ 100–200 bars, close to the actual well measurements. Finally, the approach proved to be an excellent tool to investigate the presence of an active geothermal reservoir at depth and that the H2‐CO2‐CH4‐CO‐Ar gas composition is a useful T‐P geochemical indicator for such CO2 rich geothermal systems.
Effects of cloud‐radiative heating on atmospheric general circulation model (AGCM) simulations of convectively coupled equatorial waves
Authors: Lin Jia‐Lin , Kim Daehyun , Lee Myong‐In , Kang In‐Sik
Published: December 2007

This study examines the effects of cloud‐radiative heating on convectively coupled equatorial waves simulated by the Seoul National University (SNU) atmospheric general circulation model (AGCM). The strength of cloud‐radiative heating is adjusted by modifying the autoconversion rate needed for cloud condensates to grow up to raindrops. The results show that increasing the autoconversion rate has little effect on the climatological mean precipitation, but it significantly reduces the time‐mean clouds and radiative heating in the upper troposphere and enhances heating due to moist processes in the middle troposphere. These lead to cooling of time‐mean upper troposphere temperature and drying of lower‐troposphere moisture. Reduction of cloud‐radiative heating enhances the prominence of Kelvin and n = 0 eastward inertial gravity (EIG) waves. It also tends to enhance significantly the variance of the Kelvin, equatorial Rossby (ER), mixed Rossby‐gravity (MRG), and n = 1 westward inertial gravity (WIG) waves, but not the Madden‐Julian Oscillation (MJO) or n = 0 EIG wave. Reduction of cloud‐radiative heating has little effect on the phase speed of the waves, which is associated with unchanged effective static stability caused by the near cancellation between reduced dry static stability and reduced diabatic heating. An important implication of this study is that when tuning GCM's top‐of‐the‐atmosphere radiative fluxes to fit the observations, one needs to make sure that the enhancement factor of cloud‐radiative heating at the intraseasonal timescale also fits with the observation so that the convectively coupled equatorial waves are not suppressed.
Regional differentiation in multidecadal connections between Indian monsoon rainfall and solar activity
Authors: Bhattacharyya Subarna , Narasimha Roddam
Published: December 2007

The wavelet cross spectra of the yearly sunspot index and homogeneous‐zone Indian monsoon rainfall time series are examined over the 120 a period 1871–1990 using Morlet continuous wavelets. The cross spectra of sunspot numbers with synthetic noise ensembles, including those matching the spectrum and probability distribution function of the rainfall time series, are used as reference to assess the significance of the cross spectrum between sunspot numbers and rainfall; their differences are studied using standard statistical tests. It is found particularly revealing to consider the two test periods 1878–1913 and 1933–1964, each comprising three complete solar cycles, which between them exhibit maximum contrast in solar activity since the beginning of accurate rainfall data collection in India [1871]. It is shown that the cumulative distribution of the 9–13 a band averaged cross power between sunspots and rainfall, derived from yearly values over either test period, differs from that between sunspots and spectrally matched noise in the same period at confidence levels of 99.5% or higher by the χ2 test. Further, the cross power of the sunspot index with rainfall, averaged over either test period, exceeds that with synthetic noise at z test confidence levels exceeding 99.99% over scale bands covering the 11.6 a sunspot cycle. The results further show variations across the different homogeneous rainfall zones of India, northeast India exhibiting a dramatically different phase relationship compared to the western regions of the country. The strong connections demonstrated here between Indian rainfall and solar activity are found to be organized approximately along quasi‐longitudinal bands tilting eastward at their northern end. This suggests that higher solar activity causes intensification of the Walker and Hadley circulations; the mechanisms that may be responsible and the evidence from models are briefly discussed.
Impact of horizontal groundwater flow and localized deforestation on the development of shallow temperature anomalies
Authors: Bense Victor , Beltrami Hugo
Published: December 2007

In this paper we discuss temperature anomalies that develop in the shallow subsurface as a result of localized deforestation in combination with shallow horizontal groundwater flow. Model results show how a patch‐wise pattern of deforestation at the surface induces significant lateral temperature gradients in the subsurface. Results also indicate that lateral heat transport by advection via horizontal groundwater flow becomes significant above flow rates of about 10−8 m/s. In a steady state situation, reached 1750 a after deforestation, an anomaly of 0.1 K is still present at a distance of ∼2.5 km downstream of the deforested patch at depths between 200 and 575 m for horizontal groundwater flow velocities between 10−7 m/s and 10−8 m/s, respectively. We carried out transient simulations to examine the impact of deforestation on subsurface temperatures during the last century. These experiments include a study of the effects of regional surface warming on the thermal regime of the subsurface. In these scenarios, 100 a after localized deforestation, significant temperature anomalies occur hundreds of meters downstream of the deforested areas. Results show that ground surface temperature history reconstructions based upon synthetic temperature versus depth profiles up‐ and downstream of the deforested patches fail to recover the timing and magnitude of the warming event imposed at the surface. Results from our numerical simulations indicate that lateral heat flow effects should be considered when using subsurface thermal data for constraining land surface schemes in general circulation models.
Metabolic activity and diversity of cryoconites in the Taylor Valley, Antarctica
Authors: Foreman Christine M. , Sattler Birgit , Mikucki Jill A. , Porazinska Dorota L. , Priscu John C.
Published: December 2007

Metabolic activity and biogeochemical diversity within cryoconites from the Canada, Commonwealth, Howard, and Hughes glaciers in the McMurdo Dry Valleys revealed the presence of a productive microbial refuge in this polar desert ecosystem. Fluorescent in situ hybridization showed a high percentage of Cytophaga‐Flavobacteria cells in cryoconite sediments (87.2%), while β‐Proteobacterial cells dominated the ice overlying the sediment layer (54.2%). The biomass of bacterial cells in the sediments was also greater (4.82 μgC ml−1) than that in the overlying ice (0.18 μgC ml−1) and was related to bacterial productivity (on the basis of thymidine incorporation), which ranged from 36 ng C l−1 d−1 in the overlying ice to 3329 ng C l−1 d−1 in the sediment‐containing layers. Bacteria within both the sediments and overlying ice were able to actively incorporate and respire radio‐labeled glucose, as well as 17 other dissolved organic carbon compounds. The cryoconites in the Taylor Valley support an active, diverse assemblage of organisms despite the fact that they may remain sealed from the atmosphere for decades. Given the density of the cryoconites in the dry valleys (∼4–6% of ablation zone surfaces), flushing of the cryoconites during warm years could provide a vital nutrient and organic carbon source to the surrounding polar desert.
Kinematic wave model for transient bed profiles in alluvial channels under nonequilibrium conditions
Authors: Tayfur Gokmen , Singh Vijay P.
Published: December 2007

Transient bed profiles in alluvial channels are generally modeled using diffusion (or dynamic) waves and assuming equilibrium between detachment and deposition rates. Equilibrium sediment transport can be considerably affected by an excess (or deficiency) of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure. In such situations the sediment transport process occurs under nonequilibrium conditions, and extensive changes in alluvial river morphology can take place over a relatively short period of time. Therefore the study and prediction of these changes are important for sustainable development and use of river water. This study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions. The kinematic wave theory employs a functional relation between sediment transport rate and concentration, the shear‐stress approach for flow transport capacity, and a relation between flow velocity and depth. The model satisfactorily simulated transient bed forms observed in laboratory experiments.
Satellite observations of the quasi 5‐day wave in noctilucent clouds and mesopause temperatures
Authors: von Savigny C. , Robert C. , Bovensmann H. , Burrows J. P. , Schwartz M.
Published: December 2007

We report on simultaneous measurements of the westward propagating quasi 5‐day wave in the occurrence rate of noctilucent clouds (NLCs) and the temperature field at NLC altitude during the 2005 NLC season in the northern hemisphere. NLCs are detected using SCIAMACHY/Envisat limb scattering measurements, and the temperature profiles are measured with MLS/Aura. Quasi 5‐day wave signatures are clearly identified in both physical and wavelet space. We find good general agreement in the quasi 5‐day wave activity of NLC occurrence rates and the mesopause temperature field, indicating that planetary wave signatures in the temperature field are the main driver of corresponding signatures in NLCs.
3‐methyl‐1,2,3‐butanetricarboxylic acid: An atmospheric tracer for terpene secondary organic aerosol
Authors: Szmigielski Rafal , Surratt Jason D. , Gómez‐González Yadian , Van der Veken Pieter , Kourtchev Ivan , Vermeylen Reinhilde , Blockhuys Frank , Jaoui Mohammed , Kleindienst Tadeusz E. , Lewandowski Michael , Offenberg John H. , Edney Edward O. , Seinfeld John H. , Maenhaut Willy , Claeys Magda
Published: December 2007

Highly oxygenated compounds assigned to be oxidation products of α‐pinene have recently been observed in substantial concentrations in ambient aerosols. Here, we confirm the unknown α‐pinene tracer compound with molecular weight (MW) 204 as the C8‐tricarboxylic acid 3‐methyl‐1,2,3‐butanetricarboxylic acid. Its gas and liquid chromatographic behaviors and its mass spectral characteristics in electron ionization and negative ion electrospray ionization perfectly agree with those of a synthesized reference compound. The formation of this compound is explained by further reaction of cis‐pinonic acid involving participation of the OH radical. This study illustrates that complex, multi‐generation chemistry holds for the photooxidation of α‐pinene in the presence of NOx.
Three‐dimensional shear‐wave splitting tomography in the Parkfield, California, region
Authors: Zhang Haijiang , Liu Yunfeng , Thurber Clifford , Roecker Steven
Published: December 2007

We developed a three‐dimensional (3D) shear‐wave splitting tomography method to image the spatial anisotropy distribution by back projecting shear wave splitting delay times along ray paths derived from a 3D shear velocity model, assuming the delay times are accumulated along the ray paths. The local strength of the anisotropy is indicated by a parameter of anisotropy percentage, K. Using the shear‐wave splitting delay times for 575 earthquakes measured at PASO and HRSN stations, we imaged a detailed 3D anisotropy percentage model around the San Andreas Fault Observatory at Depth (SAFOD). The anisotropy percentage model shows strong heterogeneities, consistent with the strong spatial variations in both measured delay times and fast polarization directions. The San Andreas Fault (SAF) zone is highly anisotropic down to a depth of ∼4 km and then becomes less anisotropic at greater depths. Outside the fault zone, the highly anisotropic zone extends as deep as ∼7 km, consistent with the systematic depth dependence of the average time delays. To the southwest of the SAF, the Salinian granitic block shows relatively strong anisotropic anomalies that are presumably caused by aligned microcracks consistent with the direction of the regional maximum compressive horizontal stress. To the northeast of the fault zone, a strong anisotropic anomaly between depths ∼2 and ∼4 km corresponds to a serpentinite body sandwiched between Franciscan rocks.
A radio science perspective on long‐duration meteor trails
Authors: Malhotra Akshay , Mathews John D. , Urbina Julio
Published: December 2007

Nonclassical radar meteor echoes or range spread trail echoes (RSTEs), lasting from tens of seconds to over 15 min, have been a subject of considerable interest and speculation in the community ever since they were first observed in the 1940s. Using data collected from the Jicamarca Radio Observatory 50 MHz VHF radar in June 2006, we find that many properties of RSTEs can be explained largely from a radio science perspective. On a statistical basis, RSTEs of duration >15 s are observed exclusively from scatterers in the k⊥B (k = radar wave number; B = geomagnetic field) region apparently as the result of trail evolution parallel to B, forming approximately Fresnel‐zone sized scattering regions thus narrowing the scattering pattern. This result implies that the initial irregularity structures in the meteor trail exhibit a wide scattering pattern that can be seen from anywhere in the radar beam given sufficient radar sensitivity but once the trail significantly elongates along B, it can be detected only from the k⊥B region of the radar. This conclusion has far‐reaching implications to current interpretations of instability development in RSTEs as the location of the meteoroid trajectory relative to the narrow k⊥B region strongly determines observed RSTE properties such as onset time relative to the head echo and trail lifetime as functions of altitude. That is, a RSTE event viewed by two closely spaced identical radars would have different properties. Meteoroid size, energy, and fragmentation as well as radar properties such as frequency, beam pattern, and absolute sensitivity play obvious roles as well.