SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Euclidean vector

38

The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.

Concepts: Sediment, Euclidean vector, Classical mechanics, Hypothesis, Greenland ice sheet, Observation, Glacier, Scientific method

35

Aging is the greatest risk factor for neurodegeneration, but the connection between the two processes remains opaque. This is in part for want of a rigorous way to define physiological age, as opposed to chronological age. Here we develop a comprehensive metric for physiological age inDrosophila,based on genome-wide expression profiling. We applied this metric to a model of adult-onset neurodegeneration, increased or decreased expression of the activating subunit of the Cdk5 protein kinase, encoded by the geneCdk5α, the ortholog of mammalian p35.Cdk5α-mediated degeneration was associated with a 27-150% acceleration of the intrinsic rate of aging, depending on the tissue and genetic manipulation. Gene ontology analysis and direct experimental tests revealed that affected, age-associated processes included numerous core phenotypes of neurodegeneration, including enhanced oxidative stress and impaired proteostasis. Taken together, our results suggest thatCdk5α-mediated neurodegeneration results from accelerated aging, in combination with cell-autonomous neuronal insults. These data fundamentally recast our picture of the relationship between neurodegeneration and its most prominent risk factor, natural aging.

Concepts: Rate, Signal transduction, Euclidean vector, Kinematics, Classical mechanics, DNA, Acceleration, Gene

27

Copy-move forgery is one of the most popular tampering artifacts in digital images. In this paper, we present an efficient method for copy-move forgery detection using Multiresolution Local Binary Patterns (MLBP). The proposed method is robust to geometric distortions and illumination variations of duplicated regions. Furthermore, the proposed block-based method recovers parameters of the geometric transformations. First, the image is divided into overlapping blocks and feature vectors for each block are extracted using LBP operators. The feature vectors are sorted based on lexicographical order. Duplicated image blocks are determined in the block matching step using k-d tree for more time reduction. Finally, in order to both determine the parameters of geometric transformations and remove the possible false matches, RANSAC (RANdom SAmple Consensus) algorithm is used. Experimental results show that the proposed approach is able to precisely detect duplicated regions even after distortions such as rotation, scaling, JPEG compression, blurring and noise adding.

Concepts: Match, Blocking, Euclidean vector, Block, C, Group, Computer graphics, Mathematics

25

While performing several functions, adherent cells deform their surrounding substrate via stable adhesions that connect the intracellular cytoskeleton to the extracellular matrix. The traction forces that deform the substrate are studied in mechanotrasduction because they are affected by the mechanics of the extracellular milieu. We review the development and application of two methods widely used to measure traction forces generated by cells on 2D substrates: i) traction force microscopy with polyacrylamide hydrogels and ii) calculation of traction forces with arrays of deformable microposts. Measuring forces with these methods relies on measuring substrate displacements and converting them into force. We describe approaches to determine force from displacements and elaborate on the necessary experimental conditions for this type of analysis. We emphasize device fabrication, mechanical calibration of substrates and covalent attachment of extracellular matrix proteins to substrates as key features in the design of experiments to measure cell traction forces with polyacrylamide hydrogels or microposts. We also report the challenges and achievements in integrating these methods with platforms for the mechanical stimulation of adherent cells. The approaches described here will enable new studies to understand cell mechanical outputs as a function of mechanical inputs and the understanding of mechanotransduction mechanisms.

Concepts: Euclidean vector, Force, Physics in medieval Islam, Protein, Integral, Enzyme, Cell membrane, Extracellular matrix

24

The primary role of the shoulder joint in tennis forehand drive is at the expense of the loadings undergone by this joint. Nevertheless, few studies investigated glenohumeral (GH) contact forces during forehand drives. The aim of this study was to investigate GH compressive and shearing forces during the flat and topspin forehand drives in advanced tennis players. 3D kinematics of flat and topspin forehand drives of 11 advanced tennis players were recorded. The Delft Shoulder and Elbow musculoskeletal model was implemented to assess the magnitude and orientation of GH contact forces during the forehand drives. The results showed no differences in magnitude and orientation of GH contact forces between the flat and topspin forehand drives. The estimated maximal GH contact force during the forward swing phase was 3573 ± 1383 N, which was on average 1.25 times greater than during the follow-through phase, and 5.8 times greater than during the backswing phase. Regardless the phase of the forehand drive, GH contact forces pointed towards the anterior-superior part of the glenoid therefore standing for shearing forces. Knowledge of GH contact forces during real sport tasks performed at high velocity may improve the understanding of various sport-specific adaptations and causative factors for shoulder problems.

Concepts: Normal force, Euclidean vector, Deltoid muscle, Classical mechanics, Glenohumeral joint, Force, Contact force, Shoulder

21

Many victims of blast-induced traumatic brain injury are occupants of military vehicles targeted by land mines. Recently improved vehicle designs protect these individuals against blast overpressure, leaving acceleration as the main force potentially responsible for brain injury. We recently developed a unique rat model of under-vehicle blast-induced hyperacceleration where exposure to acceleration as low as 50G acceleration force results in histopathological evidence of diffuse axonal injury and astrocyte activation, with no evidence of neuronal cell death. This study investigated the effects of much higher blast-induced accelerations (1200 to 2800G) on neuronal cell death, neuro-inflammation, behavioral deficits and mortality. Adult male rats were subjected to this range of accelerations, in the absence of exposure to blast overpressure, and evaluated over 28days for working memory (Y maze) and anxiety (elevated plus maze). In addition, brains obtained from rats at one and seven days post-injury were used for neuropathology and neurochemical assays. Sixty seven percent of rats died soon after being subjected to blasts resulting in 2800G acceleration. All rats exposed to 2400G acceleration survived and exhibited transient deficits in working memory and long-term anxiety like behaviors, while those exposed to 1200 acceleration G force only demonstrated increased anxiety. Behavioral deficits were associated with acute microglia/macrophage activation, increased hippocampal neuronal death, and reduced levels of tight junction- and synapse- associated proteins. Taken together, these results suggest that exposure of rats to high underbody blast-induced G forces results in neurologic injury accompanied by neuronal apoptosis, neuroinflammation and evidence for neurosynaptic alterations.

Concepts: Concussion, Euclidean vector, Nervous system, Psychology, Diffuse axonal injury, Brain, Neuron, Traumatic brain injury

13

Assessing facial attractiveness is a ubiquitous, inherent, and hard-wired phenomenon in everyday interactions. As such, it has highly adapted to the default way that faces are typically processed: viewing faces in upright orientation. By inverting faces, we can disrupt this default mode, and study how facial attractiveness is assessed. Faces, rotated at 90 (tilting to either side) and 180°, were rated on attractiveness and distinctiveness scales. For both orientations, we found that faces were rated more attractive and less distinctive than upright faces. Importantly, these effects were more pronounced for faces rated low in upright orientation, and smaller for highly attractive faces. In other words, the less attractive a face was, the more it gained in attractiveness by inversion or rotation. Based on these findings, we argue that facial attractiveness assessments might not rely on the presence of attractive facial characteristics, but on the absence of distinctive, unattractive characteristics. These unattractive characteristics are potentially weighed against an individual, attractive prototype in assessing facial attractiveness.

Concepts: Assessment, Rotation, Euclidean vector, Faces, Face, Physical attractiveness, Orientation

11

We recorded capture events (CEs) of the daphniid Ceriodaphnia dubia by the carnivorous Southern bladderwort with suction traps (Utricularia australis). Independent to orientation and behavior during trap triggering, the animals were successfully captured within 9 ms on average and sucked in with velocities of up to 4 m/s and accelerations of up to 2800 g. Phases of very high acceleration during onsets of suction were immediately followed by phases of similarly high deceleration (max.: -1900 g) inside the bladders, leading to immobilization of the prey which then dies. We found that traps perform a ‘forward strike’ during suction and that almost completely air-filled traps are still able to perform suction. The trigger hairs on the trapdoors can undergo strong bending deformation, which we interpret to be a safety feature to prevent fracture. Our results highlight the elaborate nature of the Utricularia suction traps which are functionally resilient and leave prey animals virtually no chance to escape.

Concepts: Classical mechanics, Trap, Trapdoor, Euclidean vector, Utricularia, Velocity, Kinematics, Acceleration

11

The barbell hip thrust may be an effective exercise for increasing horizontal force production and may thereby enhance performance in athletic movements requiring a horizontal force vector, such as horizontal jumping and sprint running. The ergogenic ability of the squat is well known. The purpose of this study was to compare the effects of six-week front squat and hip thrust programs in adolescent male athletes. Vertical jump height, horizontal jump distance, 10 m and 20 m sprint times, and isometric mid-thigh pull peak force were among the measured performance variables, in addition to front squat and hip thrust three-repetition maximum (3 RM) strength. Magnitude-based effect-sizes revealed potentially beneficial effects for the front squat in both front squat 3 RM strength and vertical jump height when compared to the hip thrust. No clear benefit for one intervention was observed for horizontal jump performance. Potentially beneficial effects were observed for the hip thrust compared to the front squat in 10 m and 20 m sprint times. The hip thrust was likely superior for improving normalized isometric mid-thigh pull strength, and very likely superior for improving hip thrust 3 RM and isometric mid-thigh pull strength. These results support the force vector theory.

Concepts: Classical mechanics, Torque, Tensile stress, Thrust, Strength training, Momentum, Euclidean vector, Force

6

Young stars are associated with prominent outflows of molecular gas. The ejection of gas is believed to remove angular momentum from the protostellar system, permitting young stars to grow by the accretion of material from the protostellar disk. The underlying mechanism for outflow ejection is not yet understood, but is believed to be closely linked to the protostellar disk. Various models have been proposed to explain the outflows, differing mainly in the region where acceleration of material takes place: close to the protostar itself (‘X-wind’, or stellar wind), in a larger region throughout the protostellar disk (disk wind), or at the interface between the two. Outflow launching regions have so far been probed only by indirect extrapolation because of observational limits. Here we report resolved images of carbon monoxide towards the outflow associated with the TMC1A protostellar system. These data show that gas is ejected from a region extending up to a radial distance of 25 astronomical units from the central protostar, and that angular momentum is removed from an extended region of the disk. This demonstrates that the outflowing gas is launched by an extended disk wind from a Keplerian disk.

Concepts: Euclidean vector, Carbon dioxide, Oxygen, Star cluster, Angular momentum, Carbon monoxide, Carbon, Star