排序方式: 共有1854条查询结果,搜索用时 15 毫秒
621.
In this paper, shock sterilization using the motions of microbubbles induced by underwater shock waves is verified experimentally. A bio-experiment is carried out using marine Vibrio sp.. Underwater shock waves are produced by electric discharge in a semi-ellipsoidal discharge reflector. The shock waves are focused to increase the pressure that the generated microbubbles are exposed to. The microbubbles are generated independently. The microbubble generator can produce microbubbles of around 50 μm diameter by means of Kelvin–Helmholz instability and Venturi effect. Propagation behavior of shock waves and generation process of microbubbles are captured by high-speed camera. The experimental results show that the supply of microbubbles increases the potential of shock sterilization. In addition, it is found that shock waves without microbubbles also have the capacity of sterilization, and this means that cavitation bubbles generated behind converging shock waves contribute to inactivating marine bacteria. 相似文献
622.
This paper presents a novel optimization-based approach for dynamic positioning (DP) of a fully actuated underwater vehicle equipped with an onboard ultrashort baseline transceiver to provide relative position information of two earth-fixed transponders near the vehicle. The DP system error is defined by the transponders’ positions compared to the desired values, which occur at the vehicle’s target pose (position and orientation). The proposed DP strategy is composed of two loops in a hierarchical structure. In the kinematic loop, the nonlinear model predictive control is used to generate the desired velocity by optimizing a cost function of the predictive trajectories under the constraints of velocity and transponder bearings over a limited time horizon. In the dynamic loop, the neural network model reference adaptive control with pseudo control hedging is utilized to ensure the asymptotical convergence of velocity tracking errors in the presence of uncertainties associated with unknown model parameters, currents and thruster dynamics. The effectiveness of the proposed control scheme is illustrated by comprehensive simulations. 相似文献
623.
Antti Talvitie 《Transportation》2008,35(3):375-393
The paper unpacks the planning process into its component parts: model, process, technique, and goals—the “good thing”. The
paper advances the concept that planning, policy-making, and organizational restructuring can be analyzed under the same framework.
Each of the four components is described and reductionist examples are presented to clarify the intention and to illustrate
the technique that the transport analyst teams employ in their work. The examples cover both successes and failures. They
point toward the enormous scientific task ahead for planning to become meaningful and relevant to the problems of today. Finally,
in the frame of the willingness to pay, the paper puts forward a case for an institutional framework for a financially autonomous road administration. Similarly
organized, administered, and managed entities are relevant also for other transport modes.
Antti Talvitie is a Professor (part time) at the Helsinki University of Technology. He has private practice as consultant and as psychoanalyst in the Washington DC area. Previously, Mr. Talvitie worked in the World Bank; was GM of Viatek Consulting Engineers in Espoo Finland; served as Director of Highway Construction and Maintenance in the Finnish Road Administration; and was Professor in the US, including Chairmanship of the Department Civil Engineering at the University of Buffalo. Mr. Talvitie holds Ph.D. in Civil Engineering from Northwestern University, Evanston, IL, and Certificate in Psychoanalysis from the Boston Graduate School of Psychoanalysis. 相似文献
Antti TalvitieEmail: |
Antti Talvitie is a Professor (part time) at the Helsinki University of Technology. He has private practice as consultant and as psychoanalyst in the Washington DC area. Previously, Mr. Talvitie worked in the World Bank; was GM of Viatek Consulting Engineers in Espoo Finland; served as Director of Highway Construction and Maintenance in the Finnish Road Administration; and was Professor in the US, including Chairmanship of the Department Civil Engineering at the University of Buffalo. Mr. Talvitie holds Ph.D. in Civil Engineering from Northwestern University, Evanston, IL, and Certificate in Psychoanalysis from the Boston Graduate School of Psychoanalysis. 相似文献
624.
This study explores the relationships between adoption and consideration of three travel-related strategy bundles (travel
maintaining/increasing, travel reducing, and major location/lifestyle change), linking them to a variety of explanatory variables.
The data for this study are the responses to a fourteen-page survey returned by nearly 1,300 commuting workers living in three
distinct San Francisco Bay area neighborhoods in May 1998. We first identified patterns of adoption and consideration among
the bundles, using pairwise correlation tests. The test results indicate that those who have adopted coping strategies continue
to seek for improvements across the spectrum of generalized cost, but perhaps most often repeating the consideration of a
previously-adopted bundle. Furthermore, we developed a multivariate probit model for individuals’ simultaneous consideration
of the three bundles. It is found that in addition to the previous adoption of the bundles, qualitative and quantitative Mobility-related
variables, Travel Attitudes, Personality, Lifestyle, Travel Liking, and Sociodemographics significantly affect individual
consideration of the strategy bundles. Overall, the results of this study give policy makers and planners insight into understanding
the dynamic nature of individuals’ responses to travel-related strategies, as well as differences between the responses to
congestion that are assumed by policy makers and those that are actually adopted by individuals.
Sangho Choo is a Research Associate at The Korea Transport Institute. His research interests include travel demand modeling, travel survey methods with GPS, and travel behavior modeling. Patricia L. Mokhtarian is a professor of Civil and Environmental Engineering, chair of the interdisciplinary Transportation Technology and Policy MS/PhD program, and Associate Director for Education of the Institute of Transportation Studies at the University of California, Davis. She has been modeling travel behavior and attitudes for more than 30 years. 相似文献
Patricia L. Mokhtarian (Corresponding author)Email: |
Sangho Choo is a Research Associate at The Korea Transport Institute. His research interests include travel demand modeling, travel survey methods with GPS, and travel behavior modeling. Patricia L. Mokhtarian is a professor of Civil and Environmental Engineering, chair of the interdisciplinary Transportation Technology and Policy MS/PhD program, and Associate Director for Education of the Institute of Transportation Studies at the University of California, Davis. She has been modeling travel behavior and attitudes for more than 30 years. 相似文献
625.
This paper presents a comprehensive econometric modelling framework for daily activity program generation. It is for day-specific
activity program generations of a week-long time span. Activity types considered are 15 generic categories of non-skeletal
and flexible activities. Under the daily time budget and non-negativity of participation rate constraints, the models predict
optimal sets of frequencies of the activities under consideration (given the average duration of each activity type). The
daily time budget considers at-home basic needs and night sleep activities together as a composite activity. The concept of
composite activity ensures the dynamics and continuity of time allocation and activity/travel behaviour by encapsulating altogether
the activity types that are not of our direct interest in travel demand modelling. Workers’ total working hours (skeletal
activity and not a part of the non-skeletal activity time budget) are considered as a variable in the models to accommodate
the scheduling effects inside the generation model of non-skeletal activities. Incorporation of previous day’s total executed
activities as variables introduces day-to-day dynamics into the activity program generation models. The possibility of zero
frequency of any specific activity under consideration is ensured by the Kuhn-Tucker optimality conditions used for formulating
the model structure. Models use the concept of random utility maximization approach to derive activity program set. Estimations
of the empirical models are done using the 2002–2003 CHASE survey data set collected in Toronto.
相似文献
Eric J. MillerEmail: |
626.
The majority of comparisons between state transportation systems do not control for characteristics that may vary greatly
between states (e.g., vehicle miles traveled). A shortcoming of such analyses is that a state’s individual characteristics
can be highly influential in determining how transportation policy is set and funds are spent. The purpose of this paper is
to extend previous efforts to create groups of similar peer states by developing a new methodological framework that incorporates
demographic, temporal, and locational variability into the peer group delineations. We collected historical data for 42 variables
on transportation infrastructure, population, economy, growth, topography and weather. To examine trends before and after
the passage of ISTEA we gathered data over two time periods: 1985 through 1990 and 1995 through 2000. Using principal components
analysis (PCA) we reduced variables into seven components, and then statistically clustered states into peer groups for each
time period based on the components and the remaining variables. We identified a range of cluster solutions and demonstrate
how cluster statistics help to describe the contextual basis behind the peer grouping. The results of this study are to provide
government agencies, researchers and the public with a systematic methodological framework for identifying peer states that
reflect similar attributes contributing to the development and maintenance of state transportation systems.
相似文献
Debbie A. Niemeier (Corresponding author)Email: |
627.
This paper analyzes transportation mode choice for short home-based trips using a 1999 activity survey from the Puget Sound
region of Washington State, U.S.A. Short trips are defined as those within the 95th percentile walking distance in the data,
here 1.40 miles (2.25 km). The mean walking distance was 0.4 miles (0.6 km). The mode distribution was automobile (75%), walk
(23%), bicycle (1%), and bus (1%). Walk and bicycle are found less likely as the individual’s age increases. People are more
likely to drive if they can or are accustomed to. People in multi-person families are less likely to walk or use bus, especially
families with children. An environment that attracts people’s interest and provides activity opportunities encourages people
to walk on short trips. Influencing people’s choice of transport mode on short trips should be an important part of efforts
encouraging the use of non-automobile alternatives.
相似文献
Gudmundur F. UlfarssonEmail: |
628.
Smrutiranjan Mohapatra 《船舶与海洋工程学报》2016,15(2):112-122
The interaction of oblique incident water waves with a small bottom deformation on a porous ocean-bed is examined analytically here within the framework of linear water wave theory. The upper surface of the ocean is assumed to be covered by an infinitely extended thin uniform elastic plate, while the lower surface is bounded by a porous bottom surface having a small deformation. By employing a simplified perturbation analysis, involving a small parameter δ(=1), which measures the smallness of the deformation, the governing Boundary Value Problem (BVP) is reduced to a simpler BVP for the first-order correction of the potential function. This BVP is solved using a method based on Green’s integral theorem with the introduction of suitable Green’s function to obtain the first-order potential, and this potential function is then utilized to calculate the first-order reflection and transmission coefficients in terms of integrals involving the shape function c(x) representing the bottom deformation. Consideration of a patch of sinusoidal ripples shows that when the quotient of twice the component of the incident field wave number propagating just below the elastic plate and the ripple wave number approaches one, the theory predicts a resonant interaction between the bed and the surface below the elastic plate. Again, for small angles of incidence, the reflected wave energy is more as compared to the other angles of incidence. It is also observed that the reflected wave energy is somewhat sensitive to the changes in the flexural rigidity of the elastic plate, the porosity of the bed and the ripple wave numbers. The main advantage of the present study is that the results for the values of reflection and transmission coefficients obtained are found to satisfy the energy-balance relation almost accurately. 相似文献
629.
Tendons vertically moor Tension-Leg Platforms (TLPs), thus, a deep understanding of physical tendon stresses requires the determination of the total axial deformation of the tendons, which is a combination of the heave, pitch, and surging responses. The vertical motion of the lateral sides of the TLP is coupled with surge and constitutes a portion of the pitch motion. Tendons are connected to the sides of the TLP; hence, the total displacement of the lateral sides is related to the total deformation of the tendons and the total axial stress. Therefore, investigating the total vertical response at the sides of the TLP is essential. The coupling between various degrees of freedom is not considered in the Response Amplitude Operator (RAO). Therefore, in frequency domain analysis, the estimated vertical RAO is incomplete. Also, in the time domain, only the heave motion at the center of TLP is typically studied; this problem needs to be addressed. In this paper, we investigate the portion of the pitch motion in the vertical response at the sides of the TLP in both the frequency and time domains. Numerical results demonstrate a significant effect of the pitch motion in the vertical motion of the edges of the TLP in some period ranges. 相似文献
630.
Currently, second generation intact stability criteria are being developed and evaluated by the International Maritime Organization (IMO). In this paper, we briefly present levels 1 and 2 assessment methods for the criteria of pure loss of stability and parametric roll failure modes. Subsequently, we show the KGmax curves associated with these criteria. We compute these curves for five different types of ships and compare them with the curves embodied in the current regulations. The results show that the safety margin ensured by the first level-1 method of calculation for both pure loss of stability and parametric roll seems to be excessive in many cases. They also show that the KGmax given by the second level-1 method and by the level-2 method may be very similar. In some cases, the level-2 method can be more conservative than the second level-1 method, which is unanticipated by the future regulation. The KGmax curves associated with parametric roll confirm that the C11 container ship is vulnerable to this failure mode. The computation of the second check coefficient of parametric roll level 2 (C2) for all possible values of KG reveals the existence of both authorized and restricted areas on the surface formed by both the draft and KG, which may replace the classical KGmax curves. In consequence, it is not sufficient to check that C2 is lower than the maximum authorized value (R PR0) for a fixed ship’s loading condition. 相似文献