Lock Operations Research Articles

Effect of ship locking on sediment oxygen uptake in impounded rivers

In the majority of large river systems, flow is regulated and/or otherwise affected by operational and management activities, such as ship locking. The effect of lock operation on sediment‐water oxygen fluxes was studied within a 12.9 km long impoundment at the Saar River (Germany) using eddy‐correlation flux measurements. The continuous observations cover a time period of nearly 5 days and 39 individual locking events. Ship locking is associated with the generation of surges propagating back and forth through the impoundment which causes strong variations of near‐bed current velocity and turbulence. These wave‐induced flow variations cause variations in sediment‐water oxygen fluxes. While the mean flux during time periods without lock operation was 0.5 ± 0.1 g m−2 d−1, it increased by about a factor of 2 to 1.0 ± 0.5 g m−2 d−1within time periods with ship locking. Following the daily schedule of lock operations, fluxes are predominantly enhanced during daytime and follow a pronounced diurnal rhythm. The driving force for the increased flux is the enhancement of diffusive transport across the sediment‐water interface by bottom‐boundary layer turbulence and perhaps resuspension. Additional means by which the oxygen budget of the impoundment is affected by lock‐induced flow variations are discussed.

A Distributed-Feedback Diode Laser Frequency Stabilized on Doppler-Free Cs $D_{1}$ Line

This paper describes a distributed-feedback laser diode system frequency stabilized by simple saturated absorption technique at 895 nm on the Cs D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> line with a linewidth narrower than 1 MHz. This laser source was developed to be used in a compact cesium atomic clock based on coherent population trapping. The frequency stability of the laser system, evaluated by measuring the beat note of two similar laser systems and characterized by Allan deviation, is measured to be lower than 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> for integration times of up to 2000 s, even achieving 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> at 200 s. This laser diode system, mounted in a mechanically stable cage system using easy-to-find commercially available components, remains in locked operation for several weeks without any problem.

Towards a beyond 1 GHz solid-state nuclear magnetic resonance: External lock operation in an external current mode for a 500 MHz nuclear magnetic resonance

Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb(3)Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a (7)Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm∕3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.

Preliminary Hybrid Modeling of the Panama Canal: Operations and Salinity Diffusion

This paper deals with the initial modeling of water salinity and its diffusion into the lakes during lock operation on the Panama Canal. A hybrid operational model was implemented using the AnyLogic software simulation environment. This was accomplished by generating an operational discrete-event simulation model and a continuous simulation model based on differential equations, which modeled the salinity diffusion in the lakes. This paper presents that unique application and includes the effective integration of lock operations and its impact on the environment.

A 90–240 MHz Hysteretic Controlled DC-DC Buck Converter With Digital Phase Locked Loop Synchronization

This paper reports a digital phase locked loop (D-PLL) based frequency locking technique for high frequency hysteretic controlled dc-dc buck converters. The proposed converter achieves constant operating frequency over a wide output voltage range, eliminating the dependence of switching frequency on duty cycle or voltage conversion range. The D-PLL is programmable over a wide range of parameters and can be synchronized to a clock reference to ensure proper frequency lock and switching operation outside undesirable power supply resonance bands. The stability and loop dynamics of the proposed converter is analyzed using an analog equivalent PLL behavioral model which describes the dc-dc converter as a voltage-controlled oscillator (VCO). We demonstrate a 90-240 MHz single phase converter with fast hysteretic control and output conversion range of 33%-80%. The converter achieves an efficiency of 80% at 180 MHz, a load response of 40 ns for a 120 mA current step and a peak-to-peak ripple less than 25 mV. The circuit was implemented in 130 nm digital CMOS process.

Diode-Pumped Soliton and Non-Soliton Mode-Locked Yb:GYSO Lasers

Diode-pumped soliton and non-soliton mode-locked Yb:(Gd1−x Yx)2SiO5(x = 0.5) lasers are demonstrated. Pulses as short as 1.4 ps are generated for the soliton mode-locked operation, with a pair of SF10 prisms as the negative dispersion elements. The central wavelength is 1056 nm and the repetition rate is 48 MHz. For the non-soliton mode locking, the output power could achieve ∼1.2 W, and the pulse width is about 20 ps. The critical pulse energy in the soliton-mode locked operation against the Q-switched mode locking is much lower than the critical pulse energy in the non-soliton mode-locked operation.

2ndStrike

Concurrency bugs are becoming increasingly prevalent in the multi-core era. Recently, much research has focused on data races and atomicity violation bugs, which are related to low-level memory accesses. However, a large number of concurrency typestate bugs such as "invalid reads to a closed file from a different thread" are under-studied. These concurrency typestate bugs are important yet challenging to study since they are mostly relevant to high-level program semantics. This paper presents 2ndStrike, a method to manifest hidden concurrency typestate bugs in software testing. Given a state machine describing correct program behavior on certain object typestates, 2ndStrike profiles runtime events related to the typestates and thread synchronization. Based on the profiling results, 2ndStrike then identifies bug candidates, each of which is a pair of runtime events that would cause typestate violation if the event order is reversed. Finally, 2ndStrike re-executes the program with controlled thread interleaving to manifest bug candidates. We have implemented a prototype of 2ndStrike on Linux and have illustrated our idea using three types of concurrency typestate bugs, including invalid file operation, invalid pointer dereference, and invalid lock operation. We have evaluated 2ndStrike with six real world bugs (including one previously unknown bug) from three open-source server and desktop programs (i.e., MySQL, Mozilla, pbzip2). Our experimental results show that 2ndStrike can effectively and efficiently manifest all six software bugs, most of which are difficult or impossible to manifest using stress testing or active testing techniques that are based on data race/atomicity violation. Additionally, 2ndStrike reports no false positives, provides detailed bug reports for each manifested bug, and can consistently reproduce the bug after manifesting it once.

2ndStrike

Concurrency bugs are becoming increasingly prevalent in the multi-core era. Recently, much research has focused on data races and atomicity violation bugs, which are related to low-level memory accesses. However, a large number of concurrency typestate bugs such as "invalid reads to a closed file from a different thread" are under-studied. These concurrency typestate bugs are important yet challenging to study since they are mostly relevant to high-level program semantics. This paper presents 2ndStrike, a method to manifest hidden concurrency typestate bugs in software testing. Given a state machine describing correct program behavior on certain object typestates, 2ndStrike profiles runtime events related to the typestates and thread synchronization. Based on the profiling results, 2ndStrike then identifies bug candidates, each of which is a pair of runtime events that would cause typestate violation if the event order is reversed. Finally, 2ndStrike re-executes the program with controlled thread interleaving to manifest bug candidates. We have implemented a prototype of 2ndStrike on Linux and have illustrated our idea using three types of concurrency typestate bugs, including invalid file operation, invalid pointer dereference, and invalid lock operation. We have evaluated 2ndStrike with six real world bugs (including one previously unknown bug) from three open-source server and desktop programs (i.e., MySQL, Mozilla, pbzip2). Our experimental results show that 2ndStrike can effectively and efficiently manifest all six software bugs, most of which are difficult or impossible to manifest using stress testing or active testing techniques that are based on data race/atomicity violation. Additionally, 2ndStrike reports no false positives, provides detailed bug reports for each manifested bug, and can consistently reproduce the bug after manifesting it once.

Deadlock and starvation free reentrant readers–writers: A case study combining model checking with theorem proving

The classic readers–writers problem has been extensively studied. This holds to a lesser degree for the reentrant version, where it is allowed to nest locking actions. Such nesting is useful when a library is created with various procedures each starting and ending with a lock operation. Allowing nesting makes it possible for these procedures to call each other. We considered an existing widely used industrial implementation of the reentrant readers–writers problem. Staying close to the original code, we modelled and analyzed it using a model checker resulting in the detection of a serious error: a possible deadlock situation. The model was improved and checked satisfactorily for a fixed number of processes. To achieve a correctness result for an arbitrary number of processes the model was converted to a specification that was proven with a theorem prover. Furthermore, we studied starvation. Using model checking we found a starvation problem. We have fixed the problem and checked the solution. Combining model checking with theorem proving appeared to be very effective in reducing the time of the verification process.

Evaluation of the ecological effects of heavy metals on the assemblages of benthic foraminifera of the canals of Aveiro (Portugal)

Aveiro is a town with 80,000 inhabitants situated in the central west coast of Portugal. It is located at the centre of the Ria de Aveiro, a coastal lagoon that functions as a multi-estuarine area. This town is crossed by several canals which are connected with lagoon channels through canal locks. The operation of the canal locks influences the hydro dynamism in Aveiro's canal and this and other human activities have left a sedimentary record. The study of these records was based on the sediments grain size and composition, mineralogy (by XRD techniques), geochemical (by ICP-MS), total organic carbon (TOC), and microfaunal (benthic foraminifera) content in 15 grab-samples collected in 2006 in Aveiro's canal. The total elemental concentrations evaluated by total digestion of the sediment fraction <2000 μm revealed the presence of “hot spots” of pollution caused by heavy metal contaminants in some Aveiro canals, related to legacies of past industrial activities. These “hot spots” have, for instance, higher available concentrations of Al, Cd, Co, Cu, Fe, Pb, Mn and Zn (evaluated by sequential chemical extractions) and are located in Paraíso, Alboi, Botirões and Cojo Canals, at sites where the sediments are finer and richer in TOC. Abiotic and biotic variables submitted to principal component analysis and cluster analysis highlights the hydrodynamics and human effects on the system and the negative influence of pollutants on the benthic organisms (foraminifera).

Experimental analysis of the locking and nonlinear regimes in lateral coupled diode lasers

The emission characteristics and the dynamics of laterally coupled diode lasers have been theoretically studied by many authors. However, little experimental work has been done on the locking and nonlinear dynamics of coupled lasers. An experimental characterization of the emission and dynamic characteristics is made by means of the spectrally resolved far field and of the relative intensity noise (RIN) spectrum. It was observed that by varying the bias conditions applied to the device it operates in: (1) locking (lasing both out-of-phase and in-phase lateral modes) or in (2) unlocking. Also it was found that, when the device is lateral locked, several nonlinear and chaotic operation regimes may occur and that the amplitude of the RIN spectrum is highly dependent on the locking conditions.

The Uelzen I Lock – Hypoplastic finite‐element analysis of cyclic loading

AbstractThe Uelzen I lock is a very suitable case to analyse the soil‐structure interaction during cyclic loading, because its plate‐rib structure is very flexible, the amplitude of the load cycles during lock operation is high and an extensive geotechnical monitoring system was installed in 1992.A 3D finite element simulation was used to predict the long‐term behaviour of the lock during cyclic loading. The main interest of the simulation was to choose an adequate constitutive law to simulate the quasi‐static cyclic behaviour of the soil. The adopted hypoplastic constitutive law with intergranular strain is briefly described in the paper. The computed results are compared with the measurements. The results of elastic‐perfect plastic Mohr‐Coulomb and hypoplastic simulations without intergranular strain are presented for comparison. Some interesting aspects are evidenced, such as the ‘stick‐slip’ reduction of the arching effect in the backfill due to cyclic loading.

Towards beyond 1 GHz NMR: Mechanism of the long-term drift of screening current-induced magnetic field in a Bi-2223 coil

The screening current-induced magnetic field in the (Bi,Pb) 2Sr 2Ca 2Cu 3O x (Bi-2223) insert coil proposed for a beyond 1 GHz nuclear magnetic resonance (NMR) spectrometer may generate a long-term field drift, resulting in a loss of field-frequency lock operation and an inability to make high resolution NMR measurements. The measured screening current-induced magnetic field of a Bi-2223 double-pancake coil exhibits a hysteresis effect at 4.2 K that is reproduced by a numerical simulation based on a finite thickness rectangular superconductor bar model. The screening current-induced field at the coil center is of opposite polarity to that generated by the coil current, and thus the apparent field intensity shows a positive drift with time. On the contrary, the field at a coil end is of the same polarity as the coil field, and the apparent field intensity decreases with time. If we wait for ∼1000 h after coil excitation, the field drift rate approaches the field decay rate of the persistent current of 10 −8 h −1, suitable for a long-term NMR measurement in a beyond 1 GHz NMR spectrometer.

Optimal sequencing in the presence of setup times for tow/barge traffic through a river lock

Queues of tow/barges form when a river lock is rendered inoperable due to lock malfunction, a tow/barge accident or adverse lock operating conditions. In this paper, we develop model formulations that allow the queue to be cleared using a number of differing objectives. Of particular interest is the presence of different setup times between successive passages of tow/barges through the lock. Dependent on the objective chosen, we are able to show that certain ordering protocols may be used to markedly reduce the sequencing search space for N tow/barges from the order of N! to 2 N . We present accompanying linear and nonlinear integer programming formulations and carry out computational experiments on a representative set of problems.

Lock gates improve passage of small‐bodied fish and crustaceans in a low gradient vertical‐slot fishway

Abstract A modified ‘lock’ mode of operation was trialled within a low‐slope (3.1%) vertical‐slot fishway to improve passage of small‐bodied (&lt;60 mm long) native fishes in the Murray River, Australia. Significantly greater numbers of three small‐bodied native fish and two crustacean species ascended the fishway during lock operation than during standard operation. Up to 9700 small‐bodied fish and crustaceans exited during the lock operation in a single 2‐h replicate. A deficiency of the temporary lock conditions was that large‐bodied fish and their young‐of‐the‐year (&gt;50 mm long) did not ascend during the study. Considerable experimental work is required at other sites and at higher fishway slopes before widespread retro‐fitting of lock gates. Nevertheless, these results highlight new options for potentially improving the ecological performance of existing pool‐type fishways and new facilities.

Towards beyond-1 GHz solution NMR: Internal 2H lock operation in an external current mode

We have commenced a project to develop a beyond-1 GHz solution NMR spectrometer using a HTS coil. Due to a small residual resistance present in the HTS conductor and joint resistance between conductors, a stable persistent current sufficient for NMR measurements is unlikely. Therefore, a current has to be supplied to the HTS coil from an external power supply. The ripple of an external power supply causes a field fluctuation which must be stabilized. In this study we show results of NMR measurements using a 500–600 MHz NMR in such an external current mode: the field fluctuations are stabilized by an internal 2H lock. The field fluctuation from the external power supply comprises a major field fluctuation component at low frequencies, 0.003–0.005 Hz, and superimposed minor field ripples at 2 Hz and 50 Hz. The former limits the time interval of the internal 2H lock, while the latter generates sidebands in the NMR spectrum. Sideband and baseline noise are controlled by appropriate selection of the feedback loop parameters of the lock. The quality of the 1D-solution NMR spectra observed in external current mode is equivalent to that obtained in persistent current mode. However, if the feedback loop time is as short as the gradient pulse width, refocusing of the NMR signal is lost and NMR peaks disappear. The 2D-NOESY and the 2D-HSQC spectra of ubiquitin in an external current mode have been acquired. The quality of the 2D spectra is equivalent to those obtained in persistent current mode; i.e. the internal 2H lock operates stably over an experimental time interval of 40–50 min. To realize a beyond-1 GHz NMR spectrometer, further investigations must be made of (i) the long term stability of a DC power supply, (ii) the enhancement of the compensation field limit for the internal 2H lock, (iii) the extension of the helium refill time interval, and (iv) a method to correct the field homogeneity in the external current mode.

Application of Model Predictive Control to a Cascade of River Power Plants

River power plants are important contributors to the over 19% of world electricity produced by hydro-electric plants. Built in the natural course of a river, they produce energy by manipulating the water discharge through their facilities. They therefore introduce fluctuations in the river's natural water level and flow, which might conflict with various constraints imposed for environmental and operational purposes. Motivated by these issues, we present in this paper the application of Model Predictive Control for regulating the turbine discharge of river power plants, taking into account environmental, navigational and economical constraints and limitations. Large disturbances caused by the operation of locks are particularly investigated, as well as the issue of reducing abrasion by keeping the frequency of turbine discharge adjustments modest.

Evaluation of Digitally Controlled PLL by Clock-Period Comparison

For a digitally controlled phase-locked loop (PLL), we evaluate the use of a clock-period comparator (CPC). In this PLL, only the frequency lock operation should be performed; however, the phase lock operation is also simultaneously achieved by performing the clock-period comparison when the phases of the reference signal and the output signal approach each other. Theoretically a lock-up operation was conducted. In addition, we succeeded in digitizing a voltage controlled oscillator (VCO) with a linear characteristic. We confirmed a phase lock operation with a slight loop characteristic through SPICE simulation.

Ship Lock as General Queuing System with Batch Arrivals and Batch Service

The real lock operations with ships and barge convoys areconsidered dependent on the transport technologies applied, ormore precisely, the kinds of ships/convoys requiring thelockage. The fleet can be divided as follows: (1) groups of singleships, (2) pushed and pulled tows of barges and (3) differentcombinations of previous systems (1) and (2). The groups ofships and tows passing through the lock have extremely stochasticcharacteristics thus forming various arrivals and setvicetime patterns. It means that uniform navigation or strongscheduling between locks and lock operations are not possibleeven though highly sophisticated equipment is at disposal.Therefore, in this paper an analytical method was developedusing bulk queuing systems for the analysis and planning oflock requirements supporting it with numerical example. Thedeveloped methodology can be applied to determine the meanqueue length of ships - convoys at lock anchorage, withoutblocking behaviour between upstream and downstream navigationfor single-lane traffic.

A data-driven waterway simulation model for inland waterway operation

A waterway network can be characterised as a large queuing system with features of two-way traffic, tow variations, chamber assignment, and tow sequencing. Since no analytical model is fully sufficient to analyse the system's complexity, a data-driven waterway simulation model is developed to evaluate the overall performance of any particular operational and investment plan by considering network interdependencies. The proposed model is verified with analytical queuing theory, and validated with available real world data. The model's portability and functionality are demonstrated through different network scenarios, various control alternatives for lock operations, and dynamic demand for traffic interactions.