The influence of whole-body vibration and postural support on activity interference in standing rail passengers

Travel time has generally been regarded as an unproductive period, representing a means-to-an-end in order to engage in activities at specific destinations. Rapid developments in mobile technology have provided people with innovative ways to multi-task and engage in meaningful activities while travelling. Rail transportation specifically, offers passengers advantages over other means of transportation as there is no need to focus on driving tasks. Due to the increase in passenger numbers and limited seating availability in train carriages, over one third of rail passengers are required to stand while travelling (DfT, 2013). The vibration to which rail passengers are exposed has been shown to interfere with the performance of activities and for standing passengers, it is often necessary to use postural supports such as holding on to grab rails or leaning on walls in order to maintain stability. The overall aim of the research is to evaluate the influence of whole-body vibration (WBV) exposure and standing posture on the performance of manual control tasks and the associated subjective workloads experienced by rail passengers. The use of supports, such as a backrest in seated postures, has been found to influence the response of the human body to WBV exposure, yet no reported studies have investigated the effects of postural supports on the response of the body in standing postures. Understanding how the body is affected in these conditions would increase the current state of knowledge on the biomechanical responses of the human body to vibration exposure and provide improved representation of standing postures within vibration standards (for example, ISO2631-4 (2001)) and guidelines for device interface design. A field study, using direct observation, was conducted to assess the behaviour of standing rail passengers and determine the characteristics of typical vibration exposures. This information provided the basis for the design of four subsequent laboratory studies. The main investigations of the laboratory studies were the influence of WBV exposure on objective performance measures, such as task completion time and error rate, and subjective workloads (for example, NASA TLX) for a range of manual control tasks. One of these laboratory studies evaluated the influence of various postural supports (for example, backrests) on the biomechanical responses of standing individuals. Measurements obtained during the field investigation indicated that the vibration exposures did not exceed the EU Physical Agents Exposure Action Value (EAV) and therefore posed little risk of injury. Vibration magnitudes in the horizontal directions (x- and y-axes) were higher than in the vertical direction (z-axis) and it was necessary for standing passengers to alter behaviours and use supports in order to maintain stability while travelling. The results of the laboratory studies indicated that in conditions where decrements in task performance occurred, the extent to which performance was degraded increased progressively with increases in vibration magnitude. There were conditions (for example, in the continuous control task and the Overhead Handle supported posture in the serial control task) where vibration exposure showed no significant influence on performance measures. This suggested that individuals were able to adapt and compensate for the added stress of vibration exposure in order to maintain performance levels however, this occurred at the expense of mental workload. The workload experienced by the participants increased with corresponding increases in magnitude. Vibration frequency-dependent effects in performance and workload were found to match the biomechanical responses (apparent mass and transmissibility) of the human body and resemble the frequency weightings described in the standards (ISO2631-1 (1997)). During the serial control task, the postures which demonstrated the greatest decrements to performance (for example, Lean Shoulder and Lean Back ) corresponded to the same postures that showed the greatest influence on the biomechanical responses of the body. It was concluded therefore, that measurements of the biomechanical responses to WBV could be used to offer predictions for the likelihood of activity interference. Consideration should however, be given to the applicability of this research before these results can be generalised to wider contexts. Further validation is recommended for future work to include different conditions in order to substantiate the findings of this research

Effects of horizontal whole-body vibration and standing posture on activity interference

Standing people are exposed to whole-body vibration in many environments. This paper investigates the effects of horizontal whole-body vibration and standing posture on task performance. Sixteen participants were exposed to random vibration (up to 4Hz), whilst performing a timed pegboard task in two standing postures. Objective and subjective indicators of performance were used. Time taken to complete the task increased progressively with increases in vibration magnitude; the fore-and-aft posture generally showed greater performance decrements and postural interruptions (>1.0ms-2 r.m.s.) than the lateral. For both postures, performance was better during y-axis vibration than during x-axis vibration. Subjective ratings showed similar trends to time data. Impairments due to dual axis exposure were well predicted using r.s.s. summation calculations based on single axis components. These results indicate that best performance for those standing in moving environments will be achieved if individuals adopt a lateral posture with the most severe vibration in the y-axis

A multi-factorial model for performance under vibration

Whole-body vibration affects drivers and passengers in vehicles. These people could be performing a variety of tasks that could be directly related to the control of the vehicle, or could be something unrelated to the vehicle. There is potential for the exposure to WBV whilst performing a task to adversely affect task performance. This paper uses two case studies to illustrate a model of performance and workload whilst exposed to vibration. It is shown that performance whilst completing a discrete task (Purdue pegboard) is easily affected by vibration, but a continuous task (steering wheel) is unaffected. However, in both cases, the self-reported workload increases with vibration. A model is presented that shows that where there is adaptive capacity of the operator, they are able to compensate for the vibration with greater control but at the cost of workload. However, beyond a coping threshold the performance will degrade

Chapter 14: Vulnerability of seabirds on the Great Barrier Reef to climate change

Seabirds are highly visible, charismatic predators in marine ecosystems that are defined as feeding exclusively at sea, in either nearshore, offshore or pelagic waters. At a conservative estimate there are approximately 0.7 billion individuals of 309 species of seabirds globally. Such high population abundance means that in all ecosystems where seabirds occur the levels of marine resources they consume are significant. Such high consumption rates also mean that seabirds play a number of important functional roles in marine ecosystems, including the transfer of nutrients from offshore and pelagic areas to islands and reefs, seed dispersal and the distribution of organic matter into lower parts of the developing soil profile (eg burrow-nesting species such as shearwaters).This is Chapter 14 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13

Reduction of toroidal rotation by fast wave power in DIII-D

The application of fast wave power in DIII-D has proven effective for both electron heating and current drive. Since the last RIF Conference FW power has been applied to advanced confinement regimes in DIII-D; negative central shear (NCS), VH- and H-modes, high {beta}{sub p}, and high-{ell}i. Typically these regimes show enhanced confinement of toroidal momentum exhibited by increased toroidal rotation velocity. Indeed, layers of large shear in toroidal velocity are associated with transport barriers. A rather common occurrence in these experiments is that the toroidal rotation velocity is decreased when the FW power is turned on, to lowest order independent of whether the antennas are phased for co or counter current drive. At present all the data is for co-injected beams. The central toroidal rotation can be reduced to 1/2 of the non-FW level. Here the authors describe the effect in NCS discharges with co-beam injection

On rr-Simple kk-Path

An $r$-simple $k$-path is a {path} in the graph of length $k$ that passes through each vertex at most $r$ times. The $r$-SIMPLE $k$-PATH problem, given a graph $G$ as input, asks whether there exists an $r$-simple $k$-path in $G$. We first show that this problem is NP-Complete. We then show that there is a graph $G$ that contains an $r$-simple $k$-path and no simple path of length greater than $4\log k/\log r$. So this, in a sense, motivates this problem especially when one's goal is to find a short path that visits many vertices in the graph while bounding the number of visits at each vertex. We then give a randomized algorithm that runs in time $$\mathrm{poly}(n)\cdot 2^{O( k\cdot \log r/r)}$$ that solves the $r$-SIMPLE $k$-PATH on a graph with $n$ vertices with one-sided error. We also show that a randomized algorithm with running time $\mathrm{poly}(n)\cdot 2^{(c/2)k/ r}$ with $c<1$ gives a randomized algorithm with running time \poly(n)\cdot 2^{cn} for the Hamiltonian path problem in a directed graph - an outstanding open problem. So in a sense our algorithm is optimal up to an $O(\log r)$ factor

Time-symmetric initial data for binary black holes in numerical relativity

We look for physically realistic initial data in numerical relativity which are in agreement with post-Newtonian approximations. We propose a particular solution of the time-symmetric constraint equation, appropriate to two momentarily static black holes, in the form of a conformal decomposition of the spatial metric. This solution is isometric to the post-Newtonian metric up to the 2PN order. It represents a non-linear deformation of the solution of Brill and Lindquist, i.e. an asymptotically flat region is connected to two asymptotically flat (in a certain weak sense) sheets, that are the images of the two singularities through appropriate inversion transformations. The total ADM mass M as well as the individual masses m_1 and m_2 (when they exist) are computed by surface integrals performed at infinity. Using second order perturbation theory on the Brill-Lindquist background, we prove that the binary's interacting mass-energy M-m_1-m_2 is well-defined at the 2PN order and in agreement with the known post-Newtonian result.Comment: 27 pages, to appear in Phys. Rev.

Magnetic force microscopy of single-domain cobalt dots patterned using interference lithography

We have fabricated arrays of Co dots of diameters 100 and 70 nm using interference lithography. Density of these arrays is 7.2x10{sup 9}/in{sup 2}. Magnetic force microscopy indicate that the Co dots are single domain with moments that can be controlled to point either in-plane or out-of-plane. Interference lithography is a process that is easily scaled to large areas and is potentially capable of high throughput. Large, uniform arrays of single-domain structures are potentially useful for high-density, low-noise data storage

Hard Instances of the Constrained Discrete Logarithm Problem

The discrete logarithm problem (DLP) generalizes to the constrained DLP, where the secret exponent $x$ belongs to a set known to the attacker. The complexity of generic algorithms for solving the constrained DLP depends on the choice of the set. Motivated by cryptographic applications, we study sets with succinct representation for which the constrained DLP is hard. We draw on earlier results due to Erd\"os et al. and Schnorr, develop geometric tools such as generalized Menelaus' theorem for proving lower bounds on the complexity of the constrained DLP, and construct sets with succinct representation with provable non-trivial lower bounds