Entwicklung von Methoden zur Messung der Elastizität von Geweben mittels statischer und dynamischer Magnetresonanz-Elastographie

Aufgrund ihres großen Schwankungsbereichs stellt die Gewebeelastizität einen interessanten Parameter für die Medizin da. In der Magnetresonanz-Tomographie (MRT) kann man durch phasensensitive Verschiebungsmessungen die mechanische Antwort eines Objekts auf eine externe Anregung messen und daraus die Elastizität bestimmen. In dieser Arbeit wurden die statische und die dynamische Methode der MR-Elastographie (MRE) in Experimenten mit Agarose-Gel-Phantomen entwickelt und erprobt. Für Verhärtungen in elastischer Umgebung konnte mit der statischen MRE das Verhältnis zwischen den entsprechenden Elastizitätsmodulen gemessen werden. Die in Agarose-Gelen bei einer Untersuchung mit der dynamischen MRE gemessenen Elastizitätsmodule lagen im Bereich von E=(9,6±0,1)�103Nm-2 bis E=(133,9±3,5)�103Nm-2. Erstmalig konnte dabei die Abhängigkeit der Phasenamplitude von der An-/Abstiegszeit der bipolaren Gradienten nachgewiesen werden. Dieser Effekt beeinflusst zwar nicht die Elastizitätsbestimmung, dafür kommt es aber zu einer zusätzlichen Reduzierung der Bewegungssensitivität bei großen Anregungsfrequenzen. So wird z.B. die Phasenamplitude auf dem verwendeten Tomographen bei der schnellst möglichen Gradientenschaltung und f=400Hz bereits um 19,2% reduziert. Anhand von Experimenten an Ex-vivo-Schweine-Muskelgewebe konnte gezeigt werden, dass eine Darstellung von mittels hochfokussierten Ultraschall erzeugten Läsionen mit beiden Methoden der MRE möglich ist. Bei der Aufnahme der radialen Scherwellen, die bei gepulster Beschallung um den Fokus auftreten, wurde ein in der Literatur bisher noch nicht beschriebener Temperatureffekt in den aufgenommenen Bildern beobachtet

Consistency and Timing of Marital Transitions and Survival During Midlife: the Role of Personality and Health Risk Behaviors

Background Marital status is associated with survival. Purpose The aims of this study are to evaluate marital history and timing on mortality during midlife, test the role of pre-marital personality, and quantify the role of health risk behaviors. Methods Cox proportional hazard models were run with varying classifications of marital history and sets of covariates. Results In fully adjusted models compared to the currently married, lifetime marital history predicts premature mortality with never married at 2.33 times risk of death and ever married at 1.64 risk of death. Midlife marital history shows that not having a partner during midlife (hazard ratio (HR) = 3.10 formerly married; HR = 2.59 remaining single) has the highest risk of death. Controlling for personality and health risk behaviors reduces but does not eliminate the impact of marital status. Conclusion Consistency of marital status during midlife suggests that lack of a partner is associated with midlife mortality

Not Alone: Tracing the Origins of Very Low Mass Stars and Brown Dwarfs Through Multiplicity Studies

The properties of multiple stellar systems have long provided important empirical constraints for star formation theories, enabling (along with several other lines of evidence) a concrete, qualitative picture of the birth and early evolution of normal stars. At very low masses (VLM; M <~ 0.1 M_sun), down to and below the hydrogen burning minimum mass, our understanding of formation processes is not as clear, with several competing theories now under consideration. One means of testing these theories is through the empirical characterization of VLM multiple systems. Here, we review the results of various VLM multiplicity studies to date. These systems can be generally characterized as closely separated (93% have projected separations Delta < 20 AU) and near equal-mass (77% have M_2/M_1 >= 0.8) occurring infrequently (perhaps 10-30%). Both the frequency and maximum separation of stellar and brown dwarf binaries steadily decrease for lower system masses, suggesting that VLM binary formation and/or evolution may be a mass-dependent process. There is evidence for a fairly rapid decline in the number of loosely-bound systems below ~0.3 M_sun, corresponding to a factor of 10-20 increase in the minimum binding energy of VLM binaries as compared to more massive stellar binaries. This wide-separation ``desert'' is present among both field (~1-5 Gyr) and older (> 100 Myr) cluster systems, while the youngest (<~10 Myr) VLM binaries, particularly those in nearby, low-density star forming regions, appear to have somewhat different systemic properties. We compare these empirical trends to predictions laid out by current formation theories, and outline future observational studies needed to probe the full parameter space of the lowest mass multiple systems.Comment: 16 pages, 7 figures, contributed chapter for Planets and Protostars V meeting (October 2005); full table of VLM binaries can be obtained at http://paperclip.as.arizona.edu/~nsiegler/VLM_binarie

Personality Structure Among Centenarians: The Georgia Centenarian Study

Background/Study Context: We demonstrate that observer-rated factor structure of personality in centenarians is congruent with the normative structure. Prevalence of cognitive impairment, which has previously been linked to changes in personality in younger samples, is high in this age group, requiring observer ratings to obtain valid data in a population-based context. Likewise, the broad range of cognitive functioning necessitates synthesis of results across multiple measures of cognitive performance. Methods and Results: Data from 161 participants in the Georgia Centenarian Study (GCS; MAge = 100.3 years, 84% women, 20% African American, 40% community-dwelling, 30% low cognitive functioning) support strong overall correspondence with reference structure (full sample: .94; higher cognitive functioning: .94; lower cognitive functioning: .90). Centenarians with lower cognitive functioning are higher on neuroticism and lower on openness to experience, agreeableness, and conscientiousness. Facet-level differences (higher N1–N6: anxiety, hostility, depression, self-consciousness, impulsiveness, vulnerability to stress; lower E1: warmth; lower O4–O6: actions, ideas, values; lower A1, A3, A4: trust, altruism, compliance; C1, C5: competence, self-discipline) are also observed. Multivariate factor-level models indicate only neuroticism of the five broad factors predicts membership in cognitively impaired group; facet-level models showed that lower-order scales from three of the five domains were significant. Centenarians with higher self-consciousness (N4), impulsiveness (N5), and deliberation (C6) but lower ideas (O5), compliance (A4), and self-discipline (C5) were more likely to be in the lower cognitive functioning category. Conclusion: Results present first normative population-based data for personality structure in centenarians and offer intriguing possibilities for the role of personality in cognitive impairment centered on neuroticism

(S)-1-(2-Chloro­phen­yl)-2-oxocyclo­hexan-1-aminium d-tartrate

In the title compound, C12H15ClNO+·C4H5O6 −, the cyclo­hexa­none ring adopts a chair conformation. The benzene ring is significantly twisted so that it is in an almost perpendicular position to the C—N bond with a CAr—CAr—C—N torsion angle of −96.5 (5)°. Intermolecular N—H⋯O and O—H⋯O hydrogen bonds are observed in the crystal structure

Neutron nuclear data measurements for criticality safety

To support the US Department of Energy Nuclear Criticality Safety Program, neutron-induced cross section experiments were performed at the Geel Electron Linear Accelerator of the Joint Research Center Site Geel, European Union. Neutron capture and transmission measurements were carried out using metallic natural cerium and vanadium samples. Together with existing data, the measured data will be used for a new evaluation and will be submitted with covariances to the ENDF/B nuclear data library

The Holy Grail: A road map for unlocking the climate record stored within Mars' polar layered deposits

In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 ​km thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to “read” the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planet’s climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered. During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers. The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 ​cm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 ​m of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below. In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record. 1. What are present and past fluxes of volatiles, dust, and other materials into and out of the polar regions? 2. How do orbital forcing and exchange with other reservoirs affect those fluxes? 3. What chemical and physical processes form and modify layers? 4. What is the timespan, completeness, and temporal resolution of the climate history recorded in the PLD

Predicting Successful Aging in a Population-Based Sample of Georgia Centenarians

Used a population-based sample (Georgia Centenarian Study, GCS), to determine proportions of centenarians reaching 100 years as (1) survivors (43%) of chronic diseases first experienced between 0–80 years of age, (2) delayers (36%) with chronic diseases first experienced between 80–98 years of age, or (3) escapers (17%) with chronic diseases only at 98 years of age or older. Diseases fall into two morbidity profiles of 11 chronic diseases; one including cardiovascular disease, cancer, anemia, and osteoporosis, and another including dementia. Centenarians at risk for cancer in their lifetime tended to be escapers (73%), while those at risk for cardiovascular disease tended to be survivors (24%), delayers (39%), or escapers (32%). Approximately half (43%) of the centenarians did not experience dementia. Psychiatric disorders were positively associated with dementia, but prevalence of depression, anxiety, and psychoses did not differ significantly between centenarians and an octogenarian control group. However, centenarians were higher on the Geriatric Depression Scale (GDS) than octogenarians. Consistent with our model of developmental adaptation in aging, distal life events contribute to predicting survivorship outcome in which health status as survivor, delayer, or escaper appears as adaptation variables late in life