Full Shift Research Articles

The impact of repeated bouts of shiftwork on rapid strength and reaction time in career firefighters

The purpose of this study was to examine the influence of repeated bouts of shiftwork on lower extremity maximal and rapid strength and reaction time in career firefighters. Thirty-five firefighters (3 females; 34.3 ± 9.1 years) performed a psychomotor vigilance test (PVT) and reactive maximal isometric strength assessment prior to and following a full shift rotation (three 24-hr on-off shifts). Reaction time (RT), maximal, absolute and normalised rapid strength (50, 100, 150, 200 ms), and PVT measures were assessed on-site. Separate linear regression models were used to evaluate the POST-PRE change in variables adjusted for BMI, age, sleep, and call duration. Early (50 ms) absolute rapid strength was the only variable significantly reduced (–25.9%; p = 0.031) following the full shift rotation. Our findings indicate that early rapid strength may be a sensitive measure in detecting work-related fatigue, despite minimal changes in sleep between work and non-work nights and a low call duration. Practitioner summary: We examined the impact of repeated shiftwork on changes in reaction time and neuromuscular function. Early rapid strength was a sensitive, portable lab assessment that feasibly measured work-related fatigue in career firefighters. Interventions that mitigate work-related fatigue may be impactful at preventing falls and/or risk of musculoskeletal injury.

Transfer Operators and Limit Laws for Typical Cocycles

We show that typical cocycles (in the sense of Bonatti and Viana) over irreducible subshifts of finite type obey several limit laws with respect to the unique equilibrium states for Hölder potentials. These include the central limit theorem and the large deviation principle. We also establish the analytic dependence of the top Lyapunov exponent on the underlying equilibrium state. The transfer operator and its spectral properties play key roles in establishing these limit laws.

Evaluation of Airborne Asbestos Concentrations Associated with the Operation and Maintenance of Brakes and Clutches on Nonautomated Heavy Equipment.

This study evaluated the potential for chrysotile asbestos exposure during maintenance and operation of older, nonautomated heavy equipment with chrysotile-containing brake and clutch linings. Recent reports indicate that such equipment may be in current use in the U.S. and other locations, including developing countries, due to its lower cost and ease of maintenance compared to newer equipment. Personal and area airborne fiber concentrations were measured for cranes with draglines during brake and clutch repair, equipment operation, shop cleanup, and clothes handling of the mechanic's coveralls over a period of three days. The range of airborne chrysotile concentrations during the complete friction band replacement process, including band removal from the equipment, friction lining replacement, and reinstallation, ranged from 0.0053 to 0.0273 f/cc (phase contrast microscopy-equivalent or PCME) over 3.3 to 6.2 hours. Additional bench work tasks, including electric wire brushing, hand sanding, riveting, and compressed air use were also performed. Full shift airborne chrysotile concentrations (6.1–8.5 hours) for all combined maintenance activities were 0.0093, 0.0414, and 0.0445 f/cc (PCME), on days 1, 2, and 3, respectively. Personal short-term samples (14–36 minutes) for lining removal, installation, wire brushing, hand sanding, and compressed air use ranged from nondetect (ND) to 0.238 f/cc (PCME), below the U.S. Occupational Safety and Health Administration's (OSHA's) 30-minute excursion limit of 1 f/cc. Short-term samples during crane operation, shop cleanup, and simulated laundry activities with the mechanic's coveralls ranged from ND to 0.01 f/cc (PCME; 15–36 minutes). The results indicated that full-shift measured airborne chrysotile concentrations during the brake and clutch maintenance activities evaluated remained below the U.S. 8-hour time-weighted average (TWA) permissible exposure limit (PEL) for asbestos of 0.1 f/cc. The results are likely to be relevant to farmers, construction workers, and vehicle maintenance workers historically, as well as today for those who choose to continue using and maintaining such equipment.

Maximal escape rate for shifts

<p style='text-indent:20px;'>We consider the shift transformation on the space of infinite sequences over a finite alphabet endowed with the invariant product measure, and examine the presence of a <i>hole</i> on the space. The holes we study are specified by the sequences that do not contain a given finite word as initial sub-string. The measure of the set of sequences that do not fall into the hole in the first <inline-formula><tex-math id="M1">\begin{document}$ n $\end{document}</tex-math></inline-formula> iterates of the shift is known to decay exponentially with <inline-formula><tex-math id="M2">\begin{document}$ n $\end{document}</tex-math></inline-formula>, and its exponential rate is called <i>escape rate</i>. In this paper we provide a complete characterization of the holes with maximal escape rate. In particular we show that, contrary to the case of equiprobable symbols, ordering the holes by their escape rate corresponds to neither the order by their measure nor by the length of the shortest periodic orbit they contain. Finally, we adapt our technique to the case of shifts endowed with Markov measures, where preliminary results show that a more intricate situation is to be expected.</p>

Expansive dynamics on profinite groups

A profinite group equipped with an expansive endomorphism is equivalent to a one-sided group shift. We show that these groups have a very restricted structure. More precisely, we show that any such group can be decomposed into a finite sequence of full one-sided group shifts and two finite groups.

On the multifractal spectrum of weighted Birkhoff averages

<p style='text-indent:20px;'>In this paper, we study the topological spectrum of weighted Birk–hoff averages over aperiodic and irreducible subshifts of finite type. We show that for a uniformly continuous family of potentials, the spectrum is continuous and concave over its domain. In case of typical weights with respect to some ergodic quasi-Bernoulli measure, we determine the spectrum. Moreover, in case of full shift and under the assumption that the potentials depend only on the first coordinate, we show that our result is applicable for regular weights, like Möbius sequence.</p>

Differentiability of the pressure in non-compact spaces

Regularity properties of the pressure are related to phase transitions. In this article we study thermodynamic formalism for systems defined in non-compact phase spaces, our main focus being countable Markov shifts. We produce metric compactifications of

Cohomology groups, continuous full groups and continuous orbit equivalence of topological Markov shifts

<p style='text-indent:20px;'>We will study several subgroups of continuous full groups of one-sided topological Markov shifts from the view points of cohomology groups of full group actions on the shift spaces. We also study continuous orbit equivalence and strongly continuous orbit equivalence in terms of these subgroups of the continuous full groups and the cohomology groups.</p>

Weak Formulation of the Laplacian on the Full Shift Space

We consider a Laplacian on the one-sided full shift space over a finite symbol set, which is constructed as a renormalized limit of finite difference operators. We propose a weak definition of this Laplacian, analogous to the one in calculus, by choosing test functions as those which have finite energy and vanish on various boundary sets. In the abstract setting of the shift space, the boundary sets are chosen to be the sets on which the finite difference operators are defined. We then define the Neumann derivative of functions on these boundary sets and establish a relation between three important concepts in analysis so far, namely, the Laplacian, the bilinear energy form and the Neumann derivative of a function. As a result, we obtain the Gauss-Green's formula analogous to the one in classical case. We conclude this paper by providing a sufficient condition for the Neumann boundary value problem on the shift space.

Developmental abnormalities and growth patterns in juvenile Oreochromis mossambicus chronically exposed to efavirenz

Efavirenz is an antiretroviral drug (ARV) used for the treatment of Human Immunodeficiency Virus (HIV/AIDS) infections. The effects efavirenz may have on mammals is known, however, little is known about the effects on non-target aquatic organisms, especially on growth and development of fish. Adult Oreochromis mossambicus were bred to produce newly fertilised eggs. These eggs were exposed to efavirenz using two concentrations (10.3 ng/L and 20.6 ng/L) over 60 days growth period. The growing juveniles were kept in a static renewal system under controlled laboratory conditions (27 ± 1 °C; day:night photoperiod of 14:10) to simulate an optimal growth environment similar to summer. The endpoints included changes in growth, growth rates and morphological development based on exposure to efavirenz. After morphological analyses were done at (i) 1-day post hatching, (ii) approximately two weeks post hatching, (iii) 30 days post hatching and (iv) 60 days post hatching abnormalities were reported. Efavirenz had no noticeable effect on length and weight, or growth parameters of the juveniles at all stages. Efavirenz however, influenced the morphological development of the juveniles by causing physical abnormalities (p > 0.05). Abnormalities included spinal deformities and alterations to the shape of the jaws.

Evaluation of silver nanoparticle acute and chronic effects on freshwater amphipod (Hyalella azteca).

Silver nanoparticles (AgNPs) are known to cause ecotoxic effects, but there are no existing derived ambient water quality criteria (AWQC) for these nanomaterials to protect freshwater aquatic life due to insufficient toxicological data. We exposed Hyalella azteca to silver nitrate, citrate-coated AgNPs (citrate-AgNPs), and polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs) in a 10-day and 28-day water-only static renewal system with clean sand as a substrate for the amphipods and compared their point estimates with the United States Environmental Protection Agency (USEPA) AWQC for silver. We observed that all treatments decreased the survival, growth, and biomass of H. azteca, and the order of toxicity was AgNO3 > citrate-AgNPs > PVP-AgNPs. The LC50s of AgNO3, citrate-AgNPs, and PVP-AgNPs were 3.0, 9.6, and 296.0µg total Ag L-1, respectively, for the acute exposure and 2.4, 3.2, and 61.4µg total Ag L-1, respectively, for the chronic exposure. Acute and chronic EC20s of citrate-AgNPs ranged from 0.5 to 3.5µg total Ag L-1 while that of PVP-AgNPs ranged from 31.2 to 175µg total Ag L-1 for growth and biomass. Both Ag+ released from AgNPs and the nanoparticles contributed to the observed toxicity. The dissolution and toxicity of AgNPs were influenced by surface coating agents, particle size, and surface charge. Most point estimates for AgNPs were above AWQC for silver (4.1µg L-1) and the lowest concentration (0.12µg/L) at which Ag is expected to cause chronic adverse effects to freshwater aquatic life. Our study demonstrates that the current AWQC for silver, in general, is protective of freshwater aquatic life against AgNPs tested in the present study.

Determination of activated carbon fiber adsorption capacity for several common organic vapors: applications for respiratory protection

ABSTRACT In the context of workplace safety, activated carbon in the fiber form (i.e., activated carbon fiber, ACF) represents an alternative adsorbent to granular activated carbon (GAC) for use in organic vapor respiratory protection devices. ACFs are high surface area carbonaceous materials that are often available in a self-supporting non-woven form. The physical form of ACF suggests the potential for a filtration medium that is capable of supporting both organic vapor adsorption and particulate filtration. To study the application of these materials in respiratory protection devices, ACFs (ACFF 1200 m2/g, ACFF 1800 m2/g, and ACFF 2000 m2/g) were challenged with representative organic vapors (toluene, hexane, and methyl ethyl ketone (MEK)) at an occupationally relevant concentration (200 ppm). Breakthrough curves were generated for at least three different bed weights of adsorbent. Pressure drop (i.e., the resistance across the filtration media) was also measured to determine maximum ACF bed depths for use in respiratory protection devices. Breakthrough experiments indicate that ACFF 2000 has the highest adsorption capacity for toluene (381 mg/g), followed by ACFF 1800 and ACFF 1200 (344 mg/g and 239 mg/g, respectively). A similar trend was observed for hexane: 221 mg/g, 196 mg/g, and 146 mg/g for ACFF 2000, ACFF 1800, and ACFF 1200, respectively. ACFF 1200 showed the highest adsorption capacity for the polar adsorbate MEK (168 mg/g), followed by ACFF 1800 and ACFF 2000 (166 mg/g and 147 mg/g, respectively). Based on the constraints of pressure drop, it seems unlikely the exclusive use of ACF in a filtering facepiece respirator can provide an adsorbent mass sufficient for full shift protection against organic vapor contaminants at or above the legally enforceable permissible exposure level (PEL). Nevertheless, the incorporation of ACF into a facepiece respirator appears promising for “nuisance odor” applications; i.e., the further reduction of organic vapor concentrations when workplace exposures are already below PEL concentrations. Implications: This research brings innovation to the field of occupational health and air pollution control technology by investigating the adsorption performance of activated carbon fiber (ACF) media in the context of worker respiratory protection. ACF properties such as high specific surface area (m2/g), high permeability to airflow, and rapid adsorption kinetics make it ideal for use in thin, N95-style respirators for organic vapors. Respiratory protection is an exciting and relevant application for ACF media. A lightweight adsorbent such as ACF, if incorporated into an N95-style respirator, could potentially provide nuisance-level VOC protection in a physical form that is accessible to workers and consistent with OSHA’s voluntary use provisions for facepiece respirators. The research presented in this manuscript represents one of several steps planned in the characterization of ACF media for this particular application.

Using Passive Samplers to Track per and Polyfluoroalkyl Substances (PFAS) Emissions From the Paper Industry: Laboratory Calibration and Field Verification

Per and polyfluoroalkyl substances (PFAS) are becoming more stringently regulated and as such, a more diverse suite of environmental monitoring methods is needed. In this work a polar organic chemical integrative sampler (POCIS) with a nylon membrane and a combination of Oasis WAX and Fluoroflash® sorbents was calibrated in the laboratory and deployed in the field. A static renewal system was used to determine sampling rates for 12 PFAS which ranged between 0.69 ± 0.27 to 5.68 ± 1.80 L/day. POCIS devices were deployed for 10 days in lake Tyrifjorden, Norway which is known to be contaminated by a closed down factory producing paper products, in order to track the evolution of the PFAS contamination in a river system draining into the lake. Th sampling campaign enabled the stretch of the river which was responsible for the emissions of PFAS to lake Tyrifjorden to be identified. Freely dissolved concentrations determined with the POCIS were lowest at the site considered to reflect a diffuse PFAS contamination and highest at the site located downstream the factory. Perfluorooctanesulfonic acid (PFOS), perfluorohexanoic acid (PFHxA) and perfluorooctane sulfonamidoacetic acid (EtFOSAA) dominated the concentration profile at this site. Emissions of PFAS to lake Tyrifjorden were estimated to be 3.96 g/day for the sum of the 12 investigated PFAS.

Finiteness in polygonal billiards on hyperbolic plane

\textsc{J. Hadamard} studied the geometric properties of geodesic flows on surfaces of negative curvature, thus initiating "Symbolic Dynamics". In this article, we follow the same geometric approach to study the geodesic trajectories of billiards in "rational polygons" on the hyperbolic plane. We particularly show that the billiard dynamics resulting thus are just 'Subshifts of Finite Type' or their dense subsets. We further show that 'Subshifts of Finite Type' play a central role in subshift dynamics and while discussing the topological structure of the space of all subshifts, we demonstrate that they approximate any shift dynamics.

Switchable efficiency terahertz anomalous refraction and focusing based on graphene metasurface

In this paper, a graphene metasurface based on split-ring resonators (SRRs) structure has been proposed and investigated numerically, which can achieve the highly efficiency switchability of anomalous refraction and planar focuing effects. Numerical simulation results indicated that the proposed graphene metasurface could not only realize polarization conversion with a transmission amplitude of about 0.4, but also achieve a full 2π phase shift by changing the geometrical parameters of SRRs structure. In addition, the efficiency of the cross-polarization transmission is highly depedent on the Fermi energy level of graphene. By elaborating design of a spatially phase profile and arrangment of unit-cell structure, anomalous refraction and planar focusing effect can be achieved, and the efficiencies are also switched by only changing the Fermi energy level rather than the physical size. It could be believed that the effective switchable graphene metasurface would lead a new path for controling the wavefront of THz waves.

A fast method for simultaneous reconstruction and segmentation in X-ray CT application

In this paper, we propose a new method to solve the minimization problem in a simultaneous reconstruction and segmentation (SRS) model for X-ray computed tomography (CT). The SRS model uses Bayes' rule and the maximum a posteriori (MAP) estimate on the hidden Markov measure field model (HMMFM). The original method [Romanov M, Dahl AB, Dong Y, Hansen PC. Simultaneous tomographic reconstruction and segmentation with class priors. Inverse Problems Sci Eng. 2016;24(8):1432–1453] includes a subproblem with logarithmic-summation (log-sum) term, which is non-separable to the classification index. This subproblem was solved by Frank–Wolfe algorithm, which is very time consuming especially when dealing with large-scale CT problems. The starting point of this paper is the commutativity of log-sum operations, where the log-sum problem could be transformed into a sum-log problem by introducing an auxiliary variable. The corresponding sum-log problem for the SRS model is separable. By applying the primal-dual algorithm, the sum-log problem turns into several easy-to-solve convex subproblems. In addition, we introduce an improved model by adding Tikhonov regularization on the SRS model, and give some convergence results for the proposed methods. Experimental results demonstrate that the proposed methods produce comparable results compared with the original SRS method with much less CPU time.

Multi-parameter independent manipulation for flexural wave by notched metasurface

There are two severe limitations of current flexural wave metasurface based on local resonance mechanism or modal conversion method: low transmittance and only a single manipulation parameter. Inspired by the interaction between notches and flexural waves, we propose a high transmittance and multi-parameter independent manipulation metasurface composed of an array notches. Firstly, based on the phase shift accumulation method, a full 2π phase shift is achieved by modulating four notch parameters independently. Secondly, the refraction and focusing metasurfaces are designed based on the generalized Snell's law and compared with the simulation results. Finally, the designed focusing metasurfaces is validated by corresponding experiments. The four metasurfaces have a good performance for broadband flexural wave focusing, and the numerical and experimental focal lengths are in great agreement with the theoretical values. The notched metasurface provides an innovative way to manipulate flexural waves without resonators, which can be used in the applications of energy harvesting, waveguide design and ultrasonic detection.

Expansions in the Local and the Central Limit Theorems for Dynamical Systems

We study higher order expansions both in the Berry–Esséen estimate (Edgeworth expansions) and in the local limit theorems for Birkhoff sums of chaotic probability preserving dynamical systems. We establish general results under technical assumptions, discuss the verification of these assumptions and illustrate our results by different examples (subshifts of finite type, Young towers, Sinai billiards, random matrix products), including situations of unbounded observables with integrability order arbitrarily close to the optimal moment condition required in the i.i.d. setting.

Large deviation principle for the backward continued fraction expansion

We investigate stochastic properties of the backward continued fraction expansion of irrational numbers in (0,1). For the mean process associated with a real-valued observable which depends only on the first digit of the expansion, we establish the large deviation principle. For any such observable which is non-negative, we completely determine the set of minimizers of the rate function in terms of a growth rate of the observable. Our method of proof employs the thermodynamic formalism for topological Markov shifts, and a multifractal analysis of pointwise Lyapunov exponents for the Rényi map generating the backward continued fraction expansion.

Existence of Gibbs States and Maximizing Measures on a General One-Dimensional Lattice System with Markovian Structure

Consider a compact metric space $(M, d_M)$ and $X = M^{\mathbb{N}}$. We prove a Ruelle's Perron Frobenius Theorem for a class of compact subshifts with Markovian structure introduced in [Bull. Braz. Math. Soc. 45 (2014), pp. 53-72] which are defined from a continuous function $A : M \times M \to \mathbb{R}$ that determines the set of admissible sequences. In particular, this class of subshifts includes the finite Markov shifts and models where the alphabet is given by the unit circle $S^1$. Using the involution Kernel, we characterize the normalized eigenfunction of the Ruelle operator associated to its maximal eigenvalue and present an extension of its corresponding Gibbs state to the bilateral approach. From these results, we prove existence of equilibrium states and accumulation points at zero temperature in a particular class of countable Markov shifts.