Search

The SNF2h remodeler slides nucleosomes most efficiently as a dimer, yet how the two protomers avoid a tug-of-war is unclear. Furthermore, SNF2h couples histone octamer deformation to nucleosome sliding, but the underlying structural basis remains unknown. Here we present cryo-EM structures of SNF2h-nucleosome complexes with ADP-BeFx that capture two potential reaction intermediates. In one structure, histone residues near the dyad and in the H2A-H2B acidic patch, distal to the active SNF2h protomer, appear disordered. The disordered acidic patch is expected to inhibit the second SNF2h protomer, while disorder near the dyad is expected to promote DNA translocation. The other structure doesn't show octamer deformation, but surprisingly shows a 2 bp translocation. FRET studies indicate that ADP-BeFx predisposes SNF2h-nucleosome complexes for an elemental translocation step. We propose a model for allosteric control through the nucleosome, where one SNF2h protomer promotes asymmetric octamer deformation to inhibit the second protomer, while stimulating directional DNA translocation.

Early warning systems have been progressively implemented in higher education institutions to predict student performance. However, they usually fail at effectively integrating the many information sources available at universities to make more accurate and timely predictions, they often lack decision-making reasoning to motivate the reasons behind the predictions, and they are generally biased toward the general student body, ignoring the idiosyncrasies of underrepresented student populations (determined by socio-demographic factors such as race, gender, residency, or status as a freshmen, transfer, adult, or first-generation students) that traditionally have greater difficulties and performance gaps. This paper presents a multiview early warning system built with comprehensible Genetic Programming classification rules adapted to specifically target underrepresented and underperforming student populations. The system integrates many student information repositories using multiview learning to improve the accuracy and timing of the predictions. Three interfaces have been developed to provide personalized and aggregated comprehensible feedback to students, instructors, and staff to facilitate early intervention and student support. Experimental results, validated with statistical analysis, indicate that this multiview learning approach outperforms traditional classifiers. Learning outcomes will help instructors and policy-makers to deploy strategies to increase retention and improve academics.

The ATP-dependent chromatin assembly factor (ACF) spaces nucleosomes to promote formation of silent chromatin. Two copies of its ATPase subunit SNF2h bind opposite sides of a nucleosome, but how these protomers avoid competition is unknown. SNF2h senses the length of DNA flanking a nucleosome via its HAND-SANT-SLIDE (HSS) domain, yet it is unclear how this interaction enhances remodeling. Using covalently connected SNF2h dimers we show that dimerization accelerates remodeling and that the HSS contributes to communication between protomers. We further identify a nucleotide-dependent conformational change in SNF2h. In one conformation the HSS binds flanking DNA, and in another conformation the HSS engages the nucleosome core. Based on these results, we propose a model in which DNA length sensing and translocation are performed by two distinct conformational states of SNF2h. Such separation of function suggests that these activities could be independently regulated to affect remodeling outcomes.

The chromatin remodeling complex ACF helps establish the appropriate nucleosome spacing for generating repressed chromatin states. ACF activity is stimulated by two defining features of the nucleosomal substrate: a basic patch on the histone H4 N-terminal tail and the specific length of flanking DNA. However, the mechanisms by which these two substrate cues function in the ACF remodeling reaction is not well understood. Using electron paramagnetic resonance spectroscopy with spin-labeled ATP analogs to probe the structure of the ATP active site under physiological solution conditions, we identify a closed state of the ATP-binding pocket that correlates with ATPase activity. We find that the H4 tail promotes pocket closure. We further show that ATPase stimulation by the H4 tail does not require a specific structure connecting the H4 tail and the globular domain. In the case of many DNA helicases, closure of the ATP-binding pocket is regulated by specific DNA substrates. Pocket closure by the H4 tail may analogously provide a mechanism to directly couple substrate recognition to activity. Surprisingly, the flanking DNA, which also stimulates ATP hydrolysis, does not promote pocket closure, suggesting that the H4 tail and flanking DNA may be recognized in different reaction steps.

This working paper reports initial results of a set of analyses investigating differences between non-truck involved and truck-involved crashes. Data was selected from the California Department of Transportation TASAS accident reporting system. Results indicate that there are differences in primary collision factors (as assigned by the California Highway Patrol through issuance of traffic citations) between truck-involved and non-truck-involved crashes in the vicinity of freeway interchanges. "Speeding' in truck-involved crashes is cited at approximately one-half its rate for non-truck-involved crashes. Additionally, there is no statistical difference in the appearance of the "Uninvolved Motorist" TASAS party designation between truck and non-truck-involved crashes.

Traffic engineering studies such as validating Highway Capacity Manual (HCM) models require complete and reliable field data. However, the wealth of intelligent transportation systems (ITS) data is sometimes rendered useless for these purposes because of missing values in the data. Many imputation techniques have been developed in the past with virtually all of them imputing a single value for a missing datum. While this provides somewhat simple and fast estimates, it does not eliminate the possibility of producing biased results and it also fails to account for the uncertainty brought about by missing data. To overcome these limitations, a multiple imputation scheme is developed which provides multiple estimates for a missing value, simulating multiple draws from a population to estimate the unknown parameter. This paper also develops a framework of imputation which gives a broad perspective so that one can relate imputation methods to each other. DOI: 10.1061/(ASCE)0733-947X(2005)131:12(931) CE Database subject headings: Intelligent transportation systems; Traffic capacity; Data processing.

This paper describes validation results of a video image processing systems: PEEK VideoTrak 900. For this research, 12 PEEK VideoTrak 900s were installed on Interstate Highway I-75 in the Atlanta metropolitan region, and traffic movements were videotaped during several time periods. The test results showed that tracking strip type and location are critical factors in obtaining the best data accuracy. The test results showed that the system provided relatively stable speeds, but some cases showed huge volume errors. The system provided reasonable volume and speed results during the daytime, but its performance diminished during the nighttime. DOI: 10.1061/(ASCE)0733-947X(2003)129:4(462) CE Database subject headings: Imaging techniques; Vehicles; Traffic surveillance; Data collection; Traffic flow; Georgia.

Police radar is known to have an effect on the speed of drivers. This effect derives from the presence of vehicles equipped with radar detectors in the traffic stream and the reactions that the drivers of these vehicles have to radar. The level of impact on a traffic stream exposed to radar transmissions is a function of the proportion of radar detector equipped vehicles in the traffic stream, i.e., the radar detector density. Microscopic simulation can be used to model this impact. A microscopic simulator extension is proposed that allows determinations of this type to be carried out by adding the capability to model driver response to radar transmissions. This approach can also be applied to the modeling of other driver warning technologies such as changeable message signs. A case study using the proposed methodology to analyze different congestion and radar detector density levels is presented and discussed. The case study shows that the efficacy of using radar as a speed reduction strategy is a function of congestion and radar detector density, with the strategy being most effective for volumes levels between 200 and 1,400 vehicles per hour per lane. CE Database keywords: Traffic flow; Radar; Simulation; Speed control.

A signal timing policy describes operational goals applied when developing a timing plan for a system of coordinated intersections. This research investigates differences in signal timing plans resulting from implementation of five basic signal timing policies (including minimizing delay, minimizing stops, minimizing fuel consumption, maximizing coordination bandwidth, and a 'baseline' policy). Further, this research investigates differences arising from application of different techniques to achieve the same policy goal (e.g., different techniques to maximize coordination bandwidth). Volume and other traffic signal data from four traffic signal systems are collected. Various computer tools including PASSER II-90 and TRANSYT-7F are used to develop signal timing plans that emphasize each policy. For the maximum bandwidth policies, several techniques for achieving the policy goal are applied. In all cases, the resulting signal timing plans are transferred to TRANSYT-7F for comparative simulation of detailed systemwide and route-specific measures of effectiveness. Review of these measures of effectiveness provides insights into the relative success of each timing policy, and the impacts of each policy on route-specific and overall system performance. Based on these insights, general guidelines for application of signal timing tools are proposed.

Data associated with over 9000 accidents involving large trucks and combination vehicles during a two-year period on freeways in the greater Los Angeles area are analyzed relative to collision factors, accident severity, incident duration, and lane closures. Relationships between type of collision and accident characteristics are explored using log-linear models. The results point to significant differences in several immediate consequences of truck-related freeway accidents according to collision type. These differences are associated both with the severity of the accident, in terms of injuries and fatalities, and the impact of the accident on system performance, in terms of incident duration and lane closures. Hit-object and broadside collisions are the most severe types in terms of fatalities and injuries, respectively, and single-vehicle accidents are relatively more severe than two-vehicle accidents. The durations of accident incidents are found to be log-normally distributed for homogeneous groups of truck accidents, categorized according to type of collision and, in some instances, severity. The longest durations are typically associated with overturns.

This paper reports the results of an effort directed toward developing a consistent methodology to assess the impacts of traffic disruption due to major transportation reconstruction/rehabilitation projects during the period of implementation. In the approach taken by this research, state-of-the-art traffic simulation models are used to estimate the performance of the transportation system during various construction phases. Alternative construction and traffic redirection strategies designed to minimize both the direct and indirect losses associated with the construction/rehabilitation are then evaluated with the  development of a systematic, computerized procedure designed to: 1. provide for the creation and comparison of multiple and 'layered' reconstruction/rehabilitation scenarios,2. minimize the required knowledge of both the detailed interactions with the model as well as the host computer, and 3. produce meaningful, comparative outputs that assist in the selection of reasonable alternatives. The resulting modeling environment is viewed as a convenient tool to assist both the traffic engineer and the transportation planner in selection of reasonable reconstruction/rehabilitation plans and schedules.

An alternative approach to the estimation of the critical cornering speed of large combination vehicles is presented. Existing techniques are based on analytical models subject to a series of simplifying assumptions, and do not explicitly consider grades and other three-dimensional roadway features of the real problem. One result of this study indicates that these simplified models may overestimate critical cornering speed by as much as 50%. The proposed technique combines detailed simulation of the dynamics of the motion of large combination vehicles through a three-dimensional roadway, with a Monte Carlo sampling of possible vehicle configurations and component mechanical properties to produce databases for statistical analysis. This approach is applied to the study of critical cornering speed at freeway-to-freeway connectors. Databases for several samples of vehicles are generated, and a series of regression models that predict critical cornering speed is created. Results indicate that these regression models may be used to predict critical cornering speed to a high degree of accuracy. Finally, critical cornering speeds estimated using these models compare reasonably with actual speed data collected at five freeway connectors.

Meerpol, Abel. See Holiday, Billie. Melville, Herman Herman Melville. Elizabeth Hardwick. Penguin Lives. New York: Lipper/Viking, 2000. 161 pp. $Can27.99; $19.95. 'Unfortunately, the innovative qualities of Herman Melville are ones […]

Index Terms-- Electronic forum, transportation research, world wide web. I. SUMMARY TransNet is an experimental service that provides a model for the organization and electronic dissemination of transportation knowledge. TransNet is an Internet cooperative whose members will include universities that have a demonstrated interest in transportation research and that have the necessary hardware, software, and personnel to host a world wide web (WWW, or Web) site. TransNet provides the opportunity for hundreds of universities and other organizations to participate in the cooperative venture. Each host organization maintains a standard set of information services for one or more specific transportation-related research topics. This paper provides an overview of the TransNet project and describes the 'nested matrix' approach adopted for topic organization. The nine basic services (literature, research, modeling, education, agency contacts, professional forum, multimedia, Internet links, and news) that will be provided by host universities for each transportation topic are described in detail. As TransNet evolves, and as more participants begin to host topic-specific service pages, a wealth of transportation research data and information will become readily accessible electronically to all interested parties.

Traffic engineering studies such as validating Highway Capacity Manual (HCM) models require complete and reliable field data. However, the wealth of intelligent transportation systems (ITS) data is sometimes rendered useless for these purposes because of missing values in the data. Many imputation techniques have been developed in the past with virtually all of them imputing a single value for a missing datum. While this provides somewhat simple and fast estimates, it does not eliminate the possibility of producing biased results and it also fails to account for the uncertainty brought about by missing data. To overcome these limitations, a multiple imputation scheme is developed which provides multiple estimates for a missing value, simulating multiple draws from a population to estimate the unknown parameter. This paper also develops a framework of imputation which gives a broad perspective so that one can relate imputation methods to each other. [ABSTRACT FROM AUTHOR]

Reports on U.S. traffic calming strategies. Design of techniques to re-allocate trips; Changing of public travel habits; Characteristics of individual roadway design elements; Implementation of traffic calming strategies; List of potential benefits using traffic calming strategies; Categories of roadway treatments; Intersection diverters; Roundabouts; Channelization; Speed humps.

The article reports that a Chicago Park District Police Training School recently inaugurated a short-answer testing program in order to measure the effectiveness of its training course in which more than 700 police officers participate. This training course has been in existence since 1936 for all men below the rank of Captain. Each officer attends school two hours a week for alternating months between September and June. The school recesses during the summer months when the demand for police service throughout the park system is at its heaviest. The men go to school while they are off duty, and the time spent by them in school is returned to them by their commanding officers at the convenience of the service. Instruction is given separately to fourteen groups, each comprising fifty-five officers. The officers attending the school range in periods of service from recent induction to forty-two years. Attendance is compulsory until a man is sixty-four years old; at sixty-five he is automatically retired from the force.