Assessment of kinematic rock slope failures in Mudurnu Valley, Turkey

Slope instabilities are one of the most frequent natural hazards capable of causing severe failures both at regional and large scales. Mudurnu, which is settled on a steep valley, is affected by regional rock slope instabilities. These instabilities constitute a hazard and create an important risk to the community since they threaten human lives, settlement areas, and historically-important structures. In order to minimize the hazard and risk associated with slope instabilities, rock masses along the valley were characterized and the potential failure mechanisms were defined. The west side of the valley, which is the focus of the research, is characterized by Cretaceous pelagic discontinuous limestone, and is prone to complex failures. The aim of the study is to characterize the rock mass along the valley, divide the area into geomechanically-uniform sectors, define possible modes of failure (kinematics) and ultimately quantify the potential failure (kinetics) and the associated risk. For the study, in addition to the field work and scan-line survey measurements, an Unmanned Aerial Vehicle (UAV) was utilized to collect high-resolution images from problematic locations that were not accessible. Then, a point cloud of the area was generated. The images were interpreted and the resulting structural representation of the rock mass was compared with information gathered from the scan-line survey in the field. Afterwards, it was used to identify the possible modes of failure along the valley. Since seismic activity in the area is significant due to the proximity of the North Anatolian Fault Zone (NAFZ), which is the most active fault system in Turkey, dynamic loading was also considered for the stability analyses

Hazard Assessment of Meteoroid Impact for the Design of Lunar Habitats

The design of self-sustaining lunar habitats is a challenge primarily due to the Moon’s lack of atmospheric protection and hazardous environment. To assure safe habitats that will lead to further lunar and space exploration, it is necessary to assess the different hazards faced on the Moon such as meteoroid impacts, extreme temperatures, and radiation. In particular, meteoroids pose a risk to lunar structures due to their high frequency of occurrence and hypervelocity impact. Continuous meteoroid impacts can harm structural elements and vital equipment compromising the well-being of lunar inhabitants. This study is focused on the hazard conceptualization and quantification of the most frequent range of meteoroids that impact the Moon, tens of grams to few kilograms. Probabilistic frequency analysis of compiled lunar meteoroid impact data was performed to estimate impactor diameter, mass, and potentially damaging energy. Selected probabilities of exceedance and return periods were determined to establish expected meteoroid characteristics within a time frame. The estimates of meteoroid characteristics are anticipated to contribute to the structural design of lunar habitats. This study ultimately provides a risk assessment platform of meteoroid impacts to proceed forward in the colonization of the Moon

Evaluation of Radiation and Design Criteria for a Lunar Habitat

Extraterrestrial habitation has long been the object of science fiction, and experts in the fields of science and engineering have proposed many designs for a lunar base. The research conducted has focused on either structural stability, radiation protection, or meteorite-impact vulnerabilities, but rarely have these been considered together. The Resilient ExtraTerrestrial Habitats (RETH) project aims to design a lunar habitat from a hazards perspective, considering general degradation, meteorite impacts, seismic activity, radiation exposure, thermal extremes, and geomagnetic storms in addition to the physiological, psychological, and sociological aspects of astronauts living in such a habitat. Several members of the RETH team will begin the project by each quantifying an individual hazard and proposing a solution which, when combined with other members’ research, will provide specific parameters used in designing a safe, self-sustaining lunar or planetary outpost. This paper focuses on the effects of cosmic and solar radiation which can be detrimental to the health of future lunar inhabitants, and as such, quantifying the amount of radiation present in the environment is vital. Different materials such as aluminum, polyethylene, water, and regolith can provide adequate shielding with varying thickness, though the possibility of using lunar lava tubes remains open

Static and dynamic responses to hyperoxia of normal placenta across gestation with T2*-weighted sequences

OBJECTIVES: T2*-weighted sequences have been identified as non-invasive tools to study the placental oxygenation in-vivo. This study aims to investigate both static and dynamic responses to hyperoxia of the normal placenta across gestation.METHODS: We conducted a single-center prospective study including 52 uncomplicated pregnancies. Two T2*-weighted sequences were performed: T2*-relaxometry was performed before and after maternal hyperoxia. The histogram distribution of T2* values was assessed by fitting a gamma distribution as T2*~Γ(αβ). A dynamic acquisition (BOLD protocol) was also performed before and during oxygen supply, until placental oxygen saturation. The signal change over time was modeled using a sigmoid function, used to determine the intensity of enhancement (∆BOLD,%), a temporal variation coefficient (λ,min -1 , controlling the slope of the curve), and the maximal steepness (Vmax, ∆BOLD.min -1 ) of placental enhancement. RESULTS: The histogram analysis of the T2* values in normoxia showed a whole-placenta variation, with a decreasing linear trend in the mean T2* value (R= -0.83, 95% CI [-0.9, -0.71], p&lt;0.001) along with a more peaked and narrower distribution of T2* values across gestation. After maternal hyperoxia, the mean T2* ratios (mean T2* hyperoxia / mean T2* baseline ) were positively correlated with gestational age, while the other histogram parameters remained stable, suggesting a translation of the histogram towards higher values with a similar aspect. The ∆BOLD showed a non-linear increase across gestation. Conversely, the λ(min -1 ) parameter, showed an inverted trend across gestation, with a significantly weaker correlation (R = -0.33, 95% CI [-0.58, -0.02], p=0.04, R 2 = 0.1). As a combination of ∆BOLD and λ, the changes in Vmax throughout gestation were mainly influenced by the changes in ∆BOLD and resulted in a positive non-linear correlation with gestational age. CONCLUSION: Our results suggest that the decrease in the T2* placental signal over gestation does not reflect a dysfunction. The BOLD effect, representative of a free-diffusion model of oxygenation, highlights the growing differences in oxygen saturation between mother and fetus across gestation (∆BOLD), and placental permeability to oxygen (λ). This article is protected by copyright. All rights reserved.</p

Magnetic Properties of Ternary Gallides of type RNi4Ga (R = Rare earths)

The magnetic properties of RNi4Ga (R = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) compounds have been investigated. These compounds form in a hexagonal CaCu5 type structure with a space group P6/mmm. Compounds with the magnetic rare earths, R = Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm, undergo a ferromagnetic transition at 5 K, 17 K, 20 K, 19 K, 12 K, 3.5 K, 8 K and 6.5 K, respectively. The transition temperatures are smaller compared to their respective parent compounds RNi5. PrNi4Ga is paramagnetic down to 2 K. LaNi4Ga and LuNi4Ga are Pauli paramagnets. All the compounds show thermomagnetic irreversibility in the magnetically ordered state except GdNi4Ga.Comment: 14 Pages 6 Figures 1 Tabl

Development of a mathematical model for predicting electrically elicited quadriceps femoris muscle forces during isovelocity knee joint motion

<p>Abstract</p> <p>Background</p> <p>Direct electrical activation of skeletal muscles of patients with upper motor neuron lesions can restore functional movements, such as standing or walking. Because responses to electrical stimulation are highly nonlinear and time varying, accurate control of muscles to produce functional movements is very difficult. Accurate and predictive mathematical models can facilitate the design of stimulation patterns and control strategies that will produce the desired force and motion. In the present study, we build upon our previous isometric model to capture the effects of constant angular velocity on the forces produced during electrically elicited concentric contractions of healthy human quadriceps femoris muscle. Modelling the isovelocity condition is important because it will enable us to understand how our model behaves under the relatively simple condition of constant velocity and will enable us to better understand the interactions of muscle length, limb velocity, and stimulation pattern on the force produced by the muscle.</p> <p>Methods</p> <p>An additional term was introduced into our previous isometric model to predict the force responses during constant velocity limb motion. Ten healthy subjects were recruited for the study. Using a KinCom dynamometer, isometric and isovelocity force data were collected from the human quadriceps femoris muscle in response to a wide range of stimulation frequencies and patterns. % error, linear regression trend lines, and paired t-tests were used to test how well the model predicted the experimental forces. In addition, sensitivity analysis was performed using Fourier Amplitude Sensitivity Test to obtain a measure of the sensitivity of our model's output to changes in model parameters.</p> <p>Results</p> <p>Percentage RMS errors between modelled and experimental forces determined for each subject at each stimulation pattern and velocity showed that the errors were in general less than 20%. The coefficients of determination between the measured and predicted forces show that the model accounted for ~86% and ~85% of the variances in the measured force-time integrals and peak forces, respectively.</p> <p>Conclusion</p> <p>The range of predictive abilities of the isovelocity model in response to changes in muscle length, velocity, and stimulation frequency for each individual make it ideal for dynamic applications like FES cycling.</p

A Criterion for Brittle Failure of Rocks Using the Theory of Critical Distances

This paper presents a new analytical criterion for brittle failure of rocks and heavily overconsolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as the critical distance. This fracture criterion is known as the Point Method, and is part of the Theory of Critical Distances, which is utilized in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, ó0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, óc and ót. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (óc/ót=3-50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low confining stresses.The work presented was initiated during a research project on “Structural integrity assessments of notch-type defects", for the Spanish Ministry of Science and Innovation (Ref.: MAT2010-15721)

Synchrony of hand-foot coupled movements: is it attained by mutual feedback entrainment or by independent linkage of each limb to a common rhythm generator?

BACKGROUND: Synchrony of coupled oscillations of ipsilateral hand and foot may be achieved by controlling the interlimb phase difference through a crossed kinaesthetic feedback between the two limbs, or by an independent linkage of each limb cycle to a common clock signal. These alternative models may be experimentally challenged by comparing the behaviour of the two limbs when they oscillate following an external time giver, either alone or coupled together. RESULTS: Ten subjects oscillated their right hand and foot both alone and coupled (iso- or antidirectionally), paced by a metronome. Wrist and ankle angular position and Electromyograms (EMG) from the respective flexor and extensor muscles were recorded. Three phase delays were measured: i) the clk-mov delay, between the clock (metronome beat) and the oscillation peak; ii) the neur (neural) delay, between the clock and the motoneurone excitatory input, as inferred from the EMG onset; and iii) the mech (mechanical) delay between the EMG onset and the corresponding point of the limb oscillation. During uncoupled oscillations (0.4 Hz to 3.0 Hz), the mech delay increased from -7° to -111° (hand) and from -4° to -83° (foot). In contrast, the clk-mov delay remained constant and close to zero in either limb since a progressive advance of the motoneurone activation on the pacing beat (neur advance) compensated for the increasing mech delay. Adding an inertial load to either extremity induced a frequency dependent increase of the limb mechanical delay that could not be completely compensated by the increase of the neural phase advance, resulting in a frequency dependent increment of clk-mov delay of the hampered limb. When limb oscillations were iso- or antidirectionally coupled, either in the loaded or unloaded condition, the three delays did not significantly change with respect to values measured when limbs were moved separately. CONCLUSION: The absence of any significant effect of limb coupling on the measured delays suggests that during hand-foot oscillations, both iso- and antidirectionally coupled, each limb is synchronised to the common rhythm generator by a "private" position control, with no need for a crossed feedback interaction between limbs

The relation between neuromechanical parameters and Ashworth score in stroke patients

Quantifying increased joint resistance into its contributing factors i.e. stiffness and viscosity ("hypertonia") and stretch reflexes ("hyperreflexia") is important in stroke rehabilitation. Existing clinical tests, such as the Ashworth Score, do not permit discrimination between underlying tissue and reflexive (neural) properties. We propose an instrumented identification paradigm for early and tailor made interventions.BioMechanical EngineeringMechanical, Maritime and Materials Engineerin