Constrained Mobility Research Articles

Stable Isotope Study of Hunter-Gatherer-Fisher Diet, Mobility, and Intensification on the Texas Gulf Coastal Plain

The Gulf Coastal Plain of Texas was populated by hunter-gatherers from the Early Archaic (ca. 7000 B.P.) through to the Late Prehistoric period (ca. A.D. 700-1400). In order to characterize past dietary adaptations along the coast and further inland, stable isotopes of carbon and nitrogen were analyzed in preserved bone from 198 individuals from mortuary sites. In addition, 140 samples of faunal bone were analyzed to elucidate the stable isotope ecology for each region. The results indicate long-term stability in dietary adaptations with regional variation among coastal, riverine, and inland groups, including an early and, substantial, use of freshwater and marine resources. There is also evidence for constrained mobility and increasing use of plant resources within regions as populations increased in size and density.

Thermal, Optical, and Static/Dynamic Mechanical Properties of Linear‐core Crosslinked Star Polymer Blends

AbstractCore crosslinked star (CCS) polymers ae synthesized and blended with linear polymers. Constrained mobility is revealed by an increase in modulus and strength with CCS polymer concentration, while creep deformation decreases and permanent strain increases. Storage modulus, loss modulus, and glass transition temperature increase with CCS polymer concentration due to miscibility and linear‐CCS polymer “arm” interactions. Master curves shift to lower frequencies with blends that experience segmental relaxation across a broader time scale due to a range of molecular environments from linear to maximum constraints in the vicinity of the crosslinked cores. Fragility and apparent activation energy increase with CCS polymer content, while fractional free volume and volume expansion decrease. magnified image

Coordinated Targeting of Mobile Sensor Networks for Ensemble Forecast Improvement

This paper presents an efficient targeting algorithm to coordinate a team of mobile sensor platforms in order to extract information from the natural environment for the purpose of improved forecasting. This coordinated targeting is complicated by the large dimensionality of the natural dynamic systems (and thus of the decision space), as well as by the constraints in the vehicle motions. While the backward formulation developed by the present authors provides a baseline framework to efficiently address the dimensionality challenge in an unconstrained setting, the key contributions of this paper are twofold: (a) to delineate how to effectively incorporate the sensor platform constrained mobility in the targeting process and (b) to demonstrate the importance of the interteam information sharing to achieve good targeting performance. Numerical examples of simplified weather forecasting verify that the presented method renders good targeting solutions while retaining computational tractability, which is crucial for the design of sensor networks that tightly interact with, and rapidly adapt to, large-scale dynamic environments.

Mullins’ effect and damage accumulation in perfluoroelastomers

PurposeThe purpose of this paper is to develop a constitutive model in cyclic viscoplasticity of perfluoroelastomers that accounts for the Mullins effect and to determine adjustable parameters in the stress‐strain relations by fitting observations in mechanical tests.Design/methodology/approachA perfluoroelastomer with a complicated internal structure is modeled as an equivalent incompressible, permanent, non‐affine network of chains with constrained mobility. Its viscoplastic response at finite strains is treated as sliding of junctions between chains with respect to their reference positions. Damage accumulation is associated with acceleration of plastic flow of junctions driven by growth of free volume. Stress‐strain relations are derived by using the Clausius‐Duhem inequality.FindingsConstitutive equations are developed that correctly describe the mechanical behavior of perfluoroelastomers under cyclic loading with stress‐ and strain‐controlled deformation programs and arbitrary numbers of cycles. Adjustable parameters in the stress‐strain relations are found by matching experimental data in uniaxial tensile tests. Numerical simulation demonstrates that the model adequately predicts characteristic features of the Mullins effect.Originality/valueA constitutive model is derived that can be applied for description of the viscoplastic response in perfluoroelastomers at cyclic loading with complicated deformation programs and prediction of their time to failure under fatigue conditions.

Joint Sink Mobility and Routing to Maximize the Lifetime of Wireless Sensor Networks: The Case of Constrained Mobility

The longevity of wireless sensor networks (WSNs) is a major issue that impacts the application of such networks. While communication protocols are striving to save energy by acting on sensor nodes, recent results show that network lifetime can be prolonged by further involving sink mobility. As most proposals give their evidence of lifetime improvement through either (small-scale) field tests or numerical simulations on rather arbitrary cases, a theoretical understanding of the reason for this improvement and the tractability of the joint optimization problem is still missing. In this paper, we build a framework for investigating the joint sink mobility and routing problem by constraining the sink to a finite number of locations. We formally prove the NP-hardness of the problem. We also investigate the induced subproblems. In particular, we develop an efficient primal-dual algorithm to solve the subproblem involving a single sink, then we generalize this algorithm to approximate the original problem involving multiple sinks. Finally, we apply the algorithm to a set of typical topological graphs; the results demonstrate the benefit of involving sink mobility, and they also suggest the desirable moving traces of a sink.

Ibuprofen-loaded poly(ε-caprolactone) layered silicate nanocomposites prepared by hot melt extrusion

Ibuprofen loaded poly(epsilon-caprolactone) (PCL) layered silicate nanocomposites were prepared by hot-melt extrusion. The morphology and extent of dispersion of ibuprofen and layered silicate was studied using a combination of wide-angle X-ray diffraction (WAXD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Exhaustive examination across the length scales revealed the composite to have both an intercalated and exfoliated morphology. The ibuprofen was well dispersed and distributed throughout the PCL matrix. Most significantly, the static tensile and dynamic mechanical properties of PCL can be manipulated as a function of nanoclay loading and is dependent on the aspect ratio of clay platelets. The glass transition of PCL increased by up to 16 degrees C on addition of nanoclay, as determined from dynamic mechanical thermal analysis (DMTA). This behaviour was attributed to the constrained mobility of PCL chains intercalated between clay platelets and to the tethering of PCL chains by hydrogen bonding with platelet edges. As a consequence, PCL crystallisation was inhibited and confirmed from non-isothermal crystallisation experiments using differential scanning calorimetry (DSC). The fraction of PCL that was crystalline (X(c)) decreased by 15% on addition of ibuprofen and nanoclay, although the temperature of crystallisation (T(c)) did not change significantly. The dissolution of ibuprofen from PCL can be retarded by addition of layered silicates (nanoclays) to the polymer matrix.

Gender, Ethnicity, and Constrained Mobility: Insights into the Resultant Social Exclusion

I posit that a comprehensive picture of transport-related social exclusion can be drawn only by a simultaneous examination of place-based, people-based, and infrastructure and system-based exclusionary mechanisms. The overlap of these three factors has been examined here through the case study of non-Western immigrant women in Norway. It is known that immobility serves the aim of segregating roles and household responsibilities in different sociocultural domains. But what happens when these roles are operated in a society with a varying outlook? For example, how are the immigrant women of non-Western cultures dealing with constrained mobility in a modern society like Norway? Is it leading to their social exclusion? Following a combination of quantitative and qualitative research methods, this paper furthers the discussion on constrained mobility as a constitutive factor of social exclusion.

Dissemination and Harvesting of Urban Data Using Vehicular Sensing Platforms

Recent advances in vehicular communications make it possible to realize vehicular sensor networks, i.e., collaborative environments where mobile vehicles that are equipped with sensors of different nature (from toxic detectors to still/video cameras) interwork to implement monitoring applications. In particular, there is an increasing interest in proactive urban monitoring, where vehicles continuously sense events from urban streets, autonomously process sensed data (e.g., recognizing license plates), and, possibly, route messages to vehicles in their vicinity to achieve a common goal (e.g., to allow police agents to track the movements of specified cars). This challenging environment requires novel solutions with respect to those of more-traditional wireless sensor nodes. In fact, unlike conventional sensor nodes, vehicles exhibit constrained mobility, have no strict limits on processing power and storage capabilities, and host sensors that may generate sheer amounts of data, thus making already-known solutions for sensor network data reporting inapplicable. This paper describes MobEyes, which is an effective middleware that was specifically designed for proactive urban monitoring and exploits node mobility to opportunistically diffuse sensed data summaries among neighbor vehicles and to create a low-cost index to query monitoring data. We have thoroughly validated the original MobEyes protocols and demonstrated their effectiveness in terms of indexing completeness, harvesting time, and overhead. In particular, this paper includes (1) analytic models for MobEyes protocol performance and their consistency with simulation-based results, (2) evaluation of performance as a function of vehicle mobility, (3) effects of concurrent exploitation of multiple harvesting agents with single/multihop communications, (4) evaluation of network overhead and overall system stability, and (5) performance validation of MobEyes in a challenging urban tracking application where the police reconstruct the movements of a suspicious driver, e.g., by specifying the license number of a car.

WiQoSM: An Integrated QoS-Aware Mobility and User Behavior Model for Wireless Data Networks

Modeling mobility and user behavior is of fundamental importance in testing the performance of protocols for wireless data networks. Although several models have been proposed in the literature, none of them can at the same time capture important features such as geographical mobility, user-generated traffic, and the wireless technology at hand. When collectively considered, these three aspects determine the user-perceived quality-of-service (QoS) level, which, in turn, might have an influence on the mobility of those users (we call them QoS-driven users) who do not display constrained mobility patterns, but they can decide to move to less congested areas of the network in case their perceived QoS level becomes unacceptable. In this paper, we introduce the Wireless QoS-aware Mobility (WiQoSM) model, which collectively considers all of the above mentioned aspects of wireless data networks. WiQoSM is composed of 1) a user mobility model, 2) a user traffic model, 3) a wireless technology model, and 4) a QoS model. Components 1,2, and 3 provide input to the QoS model, which, in turn, can influence the mobility behavior of QoS-driven users. WiQoSM is very simple to use and configure and can be used to generate user and traffic traces at the access points (APs) composing a wireless data network. WiQoSM is shown to be able to generate traces that resemble statistical features observed in traces extracted from real-world wireless local area network (WLAN) deployments. Furthermore, WiQoSM has the nice feature of allowing the fine tuning of a disjoint set of parameters in order to influence different statistical properties of the generated traces and of providing the network designer with a high degree of flexibility in choosing network parameters such as the number of users and APs, wireless channel technology, traffic mix, and so on. Given the above features, WiQoSM can be a valuable tool in the simulation of wireless data network protocols.

The Transition to an Elongation Complex by T7 RNA Polymerase Is a Multistep Process

During the transition from an initiation complex to an elongation complex (EC), T7 RNA polymerase undergoes major conformational changes that involve reorientation of a "core" subdomain as a rigid body and extensive refolding of other elements in the 266 residue N-terminal domain. The pathway and timing of these events is poorly understood. To examine this, we introduced proline residues into regions of the N-terminal domain that become alpha-helical during the reorganization and changed the charge of a key residue that interacts with the RNA:DNA hybrid 5 bp upstream of the active site in the EC but not in the initiation complex. These alterations resulted in a diminished ability to make products >5-7 nt and/or a slow transition through this point. The results indicate that the transition to an EC is a multistep process and that the movement of the core subdomain and reorganization of certain elements in the N-terminal domain commence prior to promoter release (at 8-9 nt).

Hyperbranched Polyesters on Solid Surfaces

The interfacial behavior of third and fourth generations of hyperbranched polyesters (HBP3 and HBP4) with 32 and 64 hydroxyl-terminal groups was studied with scanning probe microscopy. The molecular adsorption on a bare silicon surface of both hyperbranched polymers was described in the terms of the Langmuir isotherm. A higher adsorption amount under an identical adsorption condition was found for lower generation HPB3. The shape of HBP3 molecules within an adsorbed layer evolved from a pancake with a thickness less than 1 nm for very low surface coverage to densely packed wormlike bilayer structures with a thickness of about 3 nm for the highest surface coverage. The molecules of the fourth generation, HBP4, hold a stable, close-to-spherical shape with a diameter of 2.5 nm throughout the entire range of surface coverage including both dense monolayers and isolated molecules. High intramolecular flexibility of HBP3 molecules as compared with constrained mobility of bulkier branches of HBP4 is considered t...

Biophysical Characterization of the Cocaine Binding Pocket in the Serotonin Transporter Using a Fluorescent Cocaine Analogue as a Molecular Reporter

To explore the biophysical properties of the binding site for cocaine and related compounds in the serotonin transporter SERT, a high affinity cocaine analogue (3beta-(4-methylphenyl)tropane-2beta-carboxylic acid N-(N-methyl-N-(4-nitrobenzo-2-oxa-1,3-diazol-7-yl)ethanolamine ester hydrochloride (RTI-233); K(I) = 14 nm) that contained the environmentally sensitive fluorescent moiety 7-nitrobenzo-2-oxa-1,3-diazole (NBD) was synthesized. Specific binding of RTI-233 to the rat serotonin transporter, purified from Sf-9 insect cells, was demonstrated by the competitive inhibition of fluorescence using excess serotonin, citalopram, or RTI-55 (2beta-carbomethoxy-3beta-(4-iodophenyl)tropane). Moreover, specific binding was evidenced by measurement of steady-state fluorescence anisotropy, showing constrained mobility of bound RTI-233 relative to RTI-233 free in solution. The fluorescence of bound RTI-233 displayed an emission maximum (lambda(max)) of 532 nm, corresponding to a 4-nm blue shift as compared with the lambda(max) of RTI-233 in aqueous solution and corresponding to the lambda(max) of RTI-233 in 80% dioxane. Collisional quenching experiments revealed that the aqueous quencher potassium iodide was able to quench the fluorescence of RTI-233 in the binding pocket (K(SV =) 1.7 m(-)(1)), although not to the same extent as free RTI-233 (K(SV =) 7.2 m(-)(1)). Conversely, the hydrophobic quencher 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) quenched the fluorescence of bound RTI-233 more efficiently than free RTI-233. These data are consistent with a highly hydrophobic microenvironment in the binding pocket for cocaine-like uptake inhibitors. However, in contrast to what has been observed for small-molecule binding sites in, for example, G protein-coupled receptors, the bound cocaine analogue was still accessible for aqueous quenching and, thus, partially exposed to solvent.

Employee Involvement, Involved Employees: Participative Work Arrangements in a White-Collar Service Occupation

Using interview and observational data from an in-depth case study, this article analyzes outcomes associated with a participative approach to work for non-unionized, white-collar service workers. It describes the organizational basis for business-service workers' limited self-management, and the way consent to self-management was constructed in the context of a decentralized, unpredictable, and often interpersonally stressful work environment. Workers' constrained mobility opportunities and work biographies are also considered as part of the explanation for consent to chaotic work arrangements.

Tracking movements of lipids and Thy1 molecules in the plasmalemma of living fibroblasts by fluorescence video microscopy with nanometer scale precision.

The lateral diffusion of 100 nm fluorescent latex microspheres (FS) bound to either N-biotinyl-phosphatidyl-ethanolamine or the glycosylphosphatidylinositol-linked protein Thy1 were monitored in the plasmalemma of primary rat fibroblasts by single particle tracking of FS centroids from digital fluorescence micrographs. A silicon intensified target camera was found to be superior to slow scan cooled CCD and intensified interline transfer CCD cameras for monitoring lateral diffusion of rapidly moving FS with nanometer level precision. To estimate the maximum tracking precision, a 4 sec-sequence comprising 120 images of FS fixed to a cover glass was obtained. The mean distance of the centroids from the origin was 7.5 +/- 0.4 nm, and no centroids were beyond 16 nm from the origin. The SIT camera was then used to track FS attached to lipids and Thy1 molecules on the surface of fibroblasts. The lateral diffusion of lipid-bound FS was unconstrained, and the ensemble averaged diffusion coefficient was 0.80 x 10(-9) cm2/sec. Thy1-bound FS existed in two mobility populations, both of which demonstrated constrained mobility. The rapidly moving population, comprising 61% of the total, had an ensemble diffusion coefficient of 6.1 x 10(-10) cm2/sec, and appeared to be restricted to domains with a mean length of about 700 nm. The slowly moving population, comprising about 39% of the total, had a diffusion coefficient of 5.7 x 10(-12) cm2/sec. These results demonstrate that nanovid can be extended to the realm of fluorescence microscopy and support previous studies indicating that while the lateral mobilities of at least some lipids are not constrained to small domains by barriers to lateral diffusion in the fibroblast plasmalemma, a peripheral membrane protein which is bound only by a lipid anchor can be prevented from diffusing freely.

Adaptive Behavior Among Very Elderly Americans

This interdisciplinary project explores the reasons some extremely old individuals successfully adapt to the adversities of old age, while other apparently vital people debilitate in response to similar challenges. To test this we recorded the health, social aspirations, and experiences of a convenience panel of twenty three very elderly community dwelling Californians over an eighteen month period. At the end of the period the average age of the participants was 89. Although there was little increase in biomedical symptoms, they reported increasing fragility and more constrained mobility. Whereas the performance of those chores assessed by Instrumental Activities of Daily Living necessitated increasing help, they seemed to successfully adapt by pragmatically adjusting their aspirations to increasing frailty and loss of mobility. Overall they reported a remarkably positive and optimistic mood status. The implications for the development of policy for this rapidly expanding population are addressed.

Adaptive Behavior Among Very Elderly Americans

This interdisciplinary project explores the reasons some extremely old individuals successfully adapt to the adversities of old age, while other apparently vital people debilitate in response to similar challenges. To test this we recorded the health, social aspirations, and experiences of a convenience panel of twenty three very elderly community dwelling Californians over an eighteen month period. At the end of the period the average age of the participants was 89. Although there was little increase in biomedical symptoms, they reported increasing fragility and more constrained mobility. Whereas the performance of those chores assessed by Instrumental Activities of Daily Living necessitated increasing help, they seemed to successfully adapt by pragmatically adjusting their aspirations to increasing frailty and loss of mobility. Overall they reported a remarkably positive and optimistic mood status. The implications for the development of policy for this rapidly expanding population are addressed.

Population Pressure, Agricultural Origins, and Cultural Evolution: Constrained Mobility or Inhibited Expansion?

Population Pressure, Agricultural Origins, and Cultural Evolution: Constrained Mobility or Inhibited Expansion?

Rational Selective Exploitation Among Americans and Chinese: General Similarity, With One Surprise

A cross-cultural experiment tested predictions regarding reward allocation decisions among subjects in the United States and Taiwan. The experiment included five independent variables—two between-subject factors (American vs. Chinese; instrumental vs. unspecified vs. social-emotional allocator orientation) and three within-subject factors (high vs. low employee competence, social skill, and mobility). In general, Americans and Chinese distributed rewards quite similarly: In both cultures, allocators distributed greater rewards to employees who were more competent and possessed greater social skill. In both cultures, instrumental allocator orientation induced stronger tendencies to base allocations on competence; social-emotional allocator orientation induced stronger tendencies to base allocations on social skill. In both cultures, subjects engaged in competence-based “rational selective exploitation”—among highly competent employees, those with greater professional mobility received larger portions of the reward pool than did counterparts with constrained mobility. In both cultures, subjects also evidenced an unexpected social-skill-based rational selective exploitation—among employees with good social skill those with greater professional mobility received larger portions of the reward pool than did counterparts with constrained mobility. However, there were a number of interactions with culture that ran contrary to our a priori predictions: We hypothesized that Americans would exhibit greater individualism by focusing on competence in allocating outcomes, and that Chinese would exhibit greater collectivism by focusing on social skill. Although Americans did attend to employee competence more than Chinese, Americans also attended to employee social skill more than Chinese. These findings are discussed in terms of an expanded conceptualization of the nature of individualism and collectivism.

Social Motives Underlying Rational Selective Exploitation: The Impact of Instrumental Versus Social‐Emotional Allocator Orientation on the Distribution of Rewards in Groups

Prior research has demonstrated that allocators frequently distribute lesser rewards to employees with constrained mobility, and that this tendency is more pronounced among more competent employees. This phenomenon is termed “rational selective exploitation.” This allocation rule is rational in that it serves to maintain membership among the most desirable group members–those who contribute most to the group's task goals–but is exploitative in that it produces an erosion of equity: Although deserving of high rewards, the outcomes of competent but entrapped employees are lower than those of their counterparts with greater mobility. Four experiments tested several predictions concerning reward allocation processes. First, allocators distributed greater rewards to more competent employees. This tendency was more pronounced under conditions of instrumental allocator orientation than under conditions of social‐emotional orientation. Second, allocators distributed greater rewards to more mobile employees. This tendency was more pronounced under conditions of instrumental orientation and constrained labor pool, and was weakly promoted by the anticipation of future allocations. Third, employee competence and employee mobility interacted; the tendency to allocate greater rewards to more mobile employees was especially pronounced among highly competent employees. This interaction of competence with mobility–the rational selective exploitation effect–was stronger under conditions of instrumental allocator orientation than under conditions of greater social‐emotional concern, and was weakly promoted by the anticipation of future allocations.

Rational selective exploitation and distress: Employee reactions to performance-based and mobility-based reward allocations.

Prior research has demonstrated that allocators frequently distribute greater rewards to persons with high professional and geographic mobility than to persons with constrained mobility, especially among the very competent. This phenomenon has been termed rational selective exploitation. Do the recipients of such allocations actually experience this distribution rule as unjust and distressing, or is it a misnomer to refer to this phenomenon as exploitation? Two studies were conducted to explore this question. Study 1 was a laboratory experiment in which we manipulated relative performance level, relative mobility level, and allocation standard: performance based versus mobility based. Study 2 was a cross-sectional survey of actual employees in which subjects reported the degree to which performance and mobility were the basis for pay decisions at their places of employment, as well as the degree to which they perceived each standard to be fair. Both studies demonstrated that people regard mobility-based allocations as less fair and more distressing than performance-based allocations. Furthermore, the degree of distress resulting from mobility-based allocations is greater among persons who are disadvantaged by that standard: among people with constrained mobility, especially those who perform at high levels. These findings provide good support for the assertion that so-called rational selective exploitation is indeed distressing to employees. Reactions to this form of distress are also explored, and the implications of these findings for the allocation process are discussed.