Lock Operations Research Articles

A Molecular Keypad Lock: A Photochemical Device Capable of Authorizing Password Entries

This paper describes a new concept in the way information can be protected at the molecular scale. By harnessing the principles of molecular Boolean logic, we have designed a molecular device that mimics the operation of an electronic keypad lock, e.g., a common security circuit used for numerous applications, in which access to an object or data is to be restricted to a limited number of persons. What distinguishes this lock from a simple molecular logic gate is the fact that its output signals are dependent not only on the proper combination of the inputs but also on the correct order by which these inputs are introduced. In other words, one needs to know the exact passwords that open this lock. The different password entries are coded by a combination of two chemical and one optical input signals, which can activate, separately, blue or green fluorescence output channels from pyrene or fluorescein fluorophores. The information in each channel is a single-bit light output signal that can be used to authorize a user, to verify authentication of a product, or to initiate a higher process. This development not only opens the way for a new class of molecular decision-making devices but also adds a new dimension of protection to existing defense technologies, such as cryptography and steganography, previously achieved with molecules.

Efficient Lock Algorithm for Shared Objects in SMP Environments

We propose a new algorithm that is effective for objects that are shared among threads but are not contended for in SMP environments. We can remove the overhead of the serialization between lock and other non-lock operations and avoid the latency of complex atomic operations in most cases. We established the safety of the algorithm by using a software tool called Spin. The experimental results from our benchmarking on an SMP machine using Intel Xeon processors revealed that our algorithm could significantly improve efficiency by 80% on average compared to using complex atomic instruction.

A ‘Less-flexibility-first’ Heuristic for the Placement of Inland Vessels in a Lock

Inland vessels move goods along waterways (canals and rivers) and they visit ports. Because of their tidal nature, vessels make use of locks to enter ports or waterways. From a port management point of view, fast access to and from the port and high utilization of locks are important objectives. Where the former relates to low inbound and outbound waiting times, the latter relates to the placement of as many vessels as possible in the lock before its operation. This article includes a case study that relates to the operation of the Van Cauwelaert lock in the port of Antwerp, Belgium. Lock operation policy is as follows: vessels wait in front of the lock for a port administrator to assign places in the lock based on knowledge of the vessels’ dimensions. As such, there is no FIFO-discipline, but a ‘group-FIFO’-discipline, i.e. if n vessels are allowed into the lock, they are the first n vessels in the arrival queue. A heuristic algorithm is formulated for the placement of vessels in the lock. This algorithm supports the decision where to place the vessel in the lock, aiming to place as many vessels as possible from the arrival queue. At the same time, it supports the decision to start a locking operation or not, based on information about vessels that are announced but which have not yet arrived at the lock's entrance. The heuristic is called a ‘less-flexibility-first’-heuristic as it looks for pseudo-placements, showing which flexibility is left for the remaining vessels after placing a vessel. This article describes the implementation of the heuristic and provides numerical examples. A comparison is made between the heuristic results and daily practice, based on real-life vessel movements through the Van Cauwelaert lock in 2002.

Laser drilling in thin materials with bursts of ns-pulses generated by stimulated Brillouin scattering (SBS)

A passively Q-switched laser with a nonlinear mirror on the basis of stimulated Brillouin scattering (SBS), generates bursts of pulses with a few 10 ns pulse duration and a separation between 20–90 μs. Percussion drilling and trepanning are performed in different materials with 1 mm thickness. The optimum parameter set of these pulse trains with regard to the burr height and ablation rate is investigated. Differences in the processing results between single pulse and multi pulse structures are discussed. In addition the laser allowed for transiently mode locked operation. Results for mode locked and merely Q-switched operation were compared.

A reset-free anti-harmonic delay-locked loop using a cycle period detector

This paper describes a new delay-locked loop (DLL) circuit that uses a replica delay line and a cycle period detector to solve the false lock problem in the conventional DLLs. The auxiliary loop in the proposed DLL monitors the lock state of the main loop by estimating the cycle period of the input clock and decides whether the main loop is in the coarse lock state or not. The auxiliary loop does not require an external reset or a start-up signal for the coarse lock operation, which is performed in the background without affecting the fine lock operation of the main loop. The proposed DLL is useful in the applications such as wide range DLLs and multiphase clock generators. The proposed DLL was implemented in 0.25-/spl mu/m mixed-mode CMOS technology and its operating frequency ranges from 30 to 200 MHz. Its cycle-to-cycle rms jitter is 12.8 ps at 133 MHz, and it dissipates 30 mW at 2.5 V.

Thin locks

Language-supported synchronization is a source of serious performance problems in many Java programs. Even single-threaded applications may spend up to half their time performing useless synchronization due to the thread-safe nature of the Java libraries. We solve this performance problem with a new algorithm that allows lock and unlock operations to be performed with only a few machine instructions in the most common cases. Our locks only require a partial word per object, and were implemented without increasing object size. We present measurements from our implementation in the JDK 1.1.2 for AIX, demonstrating speedups of up to a factor of 5 in micro-benchmarks and up to a factor of 1.7 in real programs.

Pressurized Entrained Flow Gasifiers for Biomass

A new concept for the gasification of dry lignocellulosic biomass has been developed. Special attention was paid to the process compatibility with biomass feedstocks from agriculture, mainly straw, which have a higher ash, potassium and chlorine content and a lower ash softening point than wood. The first process step is a fast pyrolysis at atmospheric pressure, which produces much condensate and only little char and gas. Pyrolysis condensate and pulverised pyrolysis char are then mixed to a slurry, containing up to 90% of the initial biomass energy. In contrast to the loose-packed original biomass the dense slurries are easily pumped and stored in tanks. From a number of regional pyrolysis plants, the slurries can be transported by rail to a large central gasification facility. Thus, the economy of scale can make possible an efficient but more complex gasification and syngas utilisation technology, to produce the most valuable products. The slurries are pumped into a slagging entrained flow gasifier and are atomised and converted to syngas at high operating temperatures and pressures, above the operating pressure of a downstream synthesis plant. At very high pressures, alternative operation of pressure locks with a low-bulk-density biomass will become too expensive. High gasification temperatures and pressures help to produce a tar-free syngas, simplify downstream gas cleaning steps and obviate intermediate compression before synthesis. To achieve a high process efficiency, the utilisation of chemical energy in synthesis products like methanol must be complemented and combined with a use of the sensible heat for electric power generation. Various chemical and engineering aspects of the new process concept are being investigated in the laboratory. A test campaign at a pressurised entrained flow gasifier with ca. 5 MW(th) slurry throughput is under preparation. A fast pyrolysis facility designed for continuous operation with several kg/h biomass throughput is under construction. Fast pyrolysis of biomass will be achieved by mixing with an excess of hot sand in a special twin screw reactor.

Stack allocation and synchronization optimizations for Java using escape analysis

This article presents an escape analysis framework for Java to determine (1) if an object is not reachable after its method of creation returns, allowing the object to be allocated on the stack, and (2) if an object is reachable only from a single thread during its lifetime, allowing unnecessary synchronization operations on that object to be removed. We introduce a new program abstraction for escape analysis, the connection graph , that is used to establish reachability relationships between objects and object references. We show that the connection graph can be succinctly summarized for each method such that the same summary information may be used in different calling contexts without introducing imprecision into the analysis. We present an interprocedural algorithm that uses the above property to efficiently compute the connection graph and identify the nonescaping objects for methods and threads. The experimental results, from a prototype implementation of our framework in the IBM High Performance Compiler for Java, are very promising. The percentage of objects that may be allocated on the stack exceeds 70% of all dynamically created objects in the user code in three out of the ten benchmarks (with a median of 19%); 11% to 92% of all mutex lock operations are eliminated in those 10 programs (with a median of 51%), and the overall execution time reduction ranges from 2% to 23% (with a median of 7%) on a 333-MHz PowerPC workstation with 512 MB memory.

Lock reservation

Because of the built-in support for multi-threaded programming, Java programs perform many lock operations. Although the overhead has been significantly reduced in the recent virtual machines, One or more atomic operations are required for acquiring and releasing an object's lock even in the fastest cases.This paper presents a novel algorithm called lock reservation . It exploits thread locality of Java locks, which claims that the locking sequence of a Java lock contains a very long repetition of a specific thread. The algorithm allows locks to be reserved for threads. When a thread attempts to acquire a lock, it can do without any atomic operation if the lock is reserved for the thread. Otherwise, it cancels the reservation and falls back to a conventional locking algorithm.We have evaluated an implementation of lock reservation in IBM's production virtual machine and compiler. The results show that it achieved performance improvements up to 53% in real Java programs.

Developing a lock operation strategy for pool lowering

The pool lowering capability of Locks and Dam I, Mississippi River, can be increased if the lock filling and emptying system is used as a discharge outlet. However, the steady state conditions of passing flow through the lock system and the conditions during the acceleration to steady state can include excessively low pressures downstream of the filling and emptying valves. A lock valve operation scheme that provided acceptable flow conditions in the lock system was developed using a numerical flow model of the lock filling and emptying systems coupled with commercial optimisation software. The flow model was validated with field data obtained at the Lock I prototype. The resulting modelling system determined the optimum valve operations to obtain steady state conditions and provided the head–discharge relationship for the lock.

Developing a lock operation strategy for pool lowering

Developing a lock operation strategy for pool lowering

Developing a lock operation strategy for pool lowering

The pool lowering capability of Locks and Dam I, Mississippi River, can be increased if the lock filling and emptying system is used as a discharge outlet. However, the steady state conditions of passing flow through the lock system and the conditions during the acceleration to steady state can include excessively low pressures downstream of the filling and emptying valves. A lock valve operation scheme that provided acceptable flow conditions in the lock system was developed using a numerical flow model of the lock filling and emptying systems coupled with commercial optimisation software. The flow model was validated with field data obtained at the Lock I prototype. The resulting modelling system determined the optimum valve operations to obtain steady state conditions and provided the head–discharge relationship for the lock.

Lesser Bear: A lightweight process library for SMP computers—scheduling mechanism without a lock operation

AbstractWe have designed and implemented a lightweight process (thread) library called ‘Lesser Bear’ for SMP computers. Lesser Bear has thread‐level parallelism and high portability. Lesser Bear executes threads in parallel by creating UNIX processes as virtual processors and a memory‐mapped file as a huge shared‐memory space. To schedule thread in parallel, the shared‐memory space has been divided into working spaces for each virtual processor, and a ready queue has been distributed.However the previous version of Lesser Bear sometimes requires a lock operation for dequeueing. We therefore proposed a scheduling mechanism that does not require a lock operation. To achieve this, each divided space forms a link topology through the queues, and we use a lock‐free algorithm for the queue operation. This mechanism is applied to Lesser Bear and evaluated by experimental results. Copyright © 2002 John Wiley & Sons, Ltd.

Lesser Bear—a light‐weight process library for SMP computers

AbstractWe have designed and implemented a light‐weight process (thread) library called ‘Lesser Bear’ for SMP computers. Lesser Bear has high portability and thread‐level parallelism. Creating UNIX processes as virtual processors and a memory‐mapped file as a huge shared‐memory space enables Lesser Bear to execute threads in parallel. Lesser Bear requires exclusive operation between peer virtual processors, and treats a shared‐memory space as a critical section for synchronization of threads. Therefore, thread functions of the previous Lesser Bear are serialized. In this paper, we present a scheduling mechanism to execute thread functions in parallel. In the design of the proposed mechanism, we divide the entire shared‐memory space into partial spaces for virtual processors, and prepare two queues (Protect Queue and Waiver Queue) for each partial space. We adopt an algorithm in which lock operations are not necessary for enqueueing. This algorithm allows us to propose a scheduling mechanism that can reduce the scheduling overhead. The mechanism is applied to Lesser Bear and evaluated by experimental results. Copyright © 2001 John Wiley & Sons, Ltd.

THE BARRIER-LOCK CLOCK: A SCALABLE SYNCHRONIZATION-ORIENTED LOGICAL CLOCK

In this article, we introduce a new logical clock, the barrier-lock clock, whose conception is based on the lazy release consistency memory model (LRC) supported by several distributed shared memory (DSM) systems. Since in the LRC, the propagation of shared memory updates performed by the processes of a parallel application is induced by lock and barrier operations, our logical clock has been modeled on those operations. Each barrier-lock times-tamp encodes the synchronization operation with which it is associated. Its size is not dependent on the number of processes of the system, as the traditional logical vector clocks, but it is proportional to the number of locks. The barrier-lock time characterizes the causality of shared memory updates performed by processes of a parallel application running on a LRC-based DSM system. A formal proof and experimental tests have confirmed such property.

Novel boom/skirt systems for improvement of water quality in estuarial impoundments subject to saline influx

The recent popularity of esturial barrage construction in the UK has been driven largely by commercial and amenity interests arising from the need to rehabilitate tracts of derelict urban land. Formation of a permanent water body to replace the tidal regime hides unsightly mud banks and facilities ready access for water based recreation. Unfortunately, in most cases, and presumably arising from upstream extreme flood risk assessment, the barrier is designed to overtop under the highest (spring) tidal peaks so allowing a substantial influx of heavier saltwater into the impoundment on a regular basis. This might well substantially exceed influx via any navigational lock operations. The problem created by the salt water is that its greater density causes stratification in the impounded water body. In times of low freshwater flow little mixing takes place and the normal action of the wind, in circulating and aerating the water body, will only extend within the lighter and often thin surface freshwater layer. The consequence is that little reoxygenation of the lower layers takes place leading to depressed dissolved oxygen levels and possible anoxia. Sluice provision in the barrage may be ineffective in expelling the saline layers, so this water remains near stagnant and deteriorates in quality due to sediment oxygen demands until a major fluvial flood, or new saline influx, is able to effectively mix the waters. Conventional continuous surface releases through fish pass and/or by crest overspill ensure the preferential release of the freshwater rather than the problematic saltwater. Retrofitting of novel low cost floating boom/skirt baffle system is proposed here for alleviation of the problem.

Queuing network analysis for waterways with artificial neural networks

An Artificial Neural Network (ANN) model has been developed for analyzing traffic in an inland waterway network. The main purpose of this paper is to determine how well such a relatively fast model for analyzing a queuing network could substitute for far more expensive simulation. Its substitutability for simulation is judged by relative discrepancies in predicting tow delays between the ANN and simulation models. This model is developed by integrating five distinct ANN submodels that predict tow headway variances at (1) merge points, (2) branching (i.e., diverging) points, (3) lock exits, and (4) link outflow points (e.g., at ports, junctions, or lock entrances), plus (5) tow queuing delays at locks. Preliminary results are shown for those five submodels and for the integrated network analysis model. Eventually, such a network analyzer should be useful for designing, selecting, sequencing, and scheduling lock improvement projects, for controlling lock operations, for system maintenance planning, and for other applications where many combinations of network characteristics must be evaluated. More generally, this method of decomposing complex queuing networks into elements that can be analyzed with ANNs and then recombined provides a promising approach for analyzing other queuing networks (e.g., in transportation, communication, computing, and production systems).

Escape analysis for Java

This paper presents a simple and efficient data flow algorithm for escape analysis of objects in Java programs to determine (i) if an object can be allocated on the stack; (ii) if an object is accessed only by a single thread during its lifetime, so that synchronization operations on that object can be removed. We introduce a new program abstraction for escape analysis, the connection graph , that is used to establish reachability relationships between objects and object references. We show that the connection graph can be summarized for each method such that the same summary information may be used effectively in different calling contexts. We present an interprocedural algorithm that uses the above property to efficiently compute the connection graph and identify the non-escaping objects for methods and threads. The experimental results, from a prototype implementation of our framework in the IBM High Performance Compiler for Java, are very promising. The percentage of objects that may be allocated on the stack exceeds 70% of all dynamically created objects in three out of the ten benchmarks (with a median of 19%), 11% to 92% of all lock operations are eliminated in those ten programs (with a median of 51%), and the overall execution time reduction ranges from 2% to 23% (with a median of 7%) on a 333 MHz PowerPC workstation with 128 MB memory.

Stability and frequency tuning of thermally loaded continuous-wave AgGaS_2 optical parametric oscillators

We analyze and investigate experimentally the output stability and the frequency tuning characteristics of weakly triply resonant silver gallium sulfide (AgGaS2) optical parametric oscillators. These oscillators are subject to thermally induced bistability and passive self-frequency-locking phenomena. The robust self-frequency-locking on a single-mode pair (thermal lock) originates from the material’s ability to correct external cavity-length perturbations, which would normally cause a mode hop, by increasing or decreasing the optical path length of the cavity through the thermo-optic effect triggered by the intracavity signal–idler power fluctuations. The Fourier frequency bandwidth of this passive servo is limited to ∼1 kHz by the thermal diffusion time constant, which is proportional to the ratio of the specific heat to the thermal conductivity Cp/Kc. A thermal feedback servo gain as high as 180 is obtained, owing to the large thermal figure of merit η=(dn/dT)/Kc of AgGaS2, leading to routine passive mode-hop-free operation for more than 30 min, without the need for an external cavity-length servo. Analysis of the stability range of the thermally loaded standing-wave resonator shows that thermal lensing is less critical for shorter doubly resonant optical parametric oscillator cavities employing shorter-curvature mirrors, in agreement with experimental observations. When a doubly resonant oscillator operates near the boundary of the power stability range a self-pulsing behavior is observed on a number of axial mode pairs. This self-pulsing is found to originate from the destabilization of a self-locked cw state, and the transition from self-pulsing to the stable self-frequency-locked state is found to be controlled by the pump frequency detuning. The passive stability allows the single-parameter frequency tuning to be studied. Under pure thermal lock operation the oscillators show a tendency to resist the pump frequency and temperature tuning processes. When an external cavity-length servo is implemented continuous tuning over 850 MHz, by means of the pump frequency tuning (Δνs/Δνp≈0.66), and over 100 MHz, by means of the crystal temperature (Δνs/ΔT≈250 MHz/°C), is obtained. These tuning ranges are in good agreement with calculations based on a cold doubly resonant oscillator.

Thin locks

Language-supported synchronization is a source of serious performance problems in many Java programs. Even single-threaded applications may spend up to half their time performing useless synchronization due to the thread-safe nature of the Java libraries. We solve this performance problem with a new algorithm that allows lock and unlock operations to be performed with only a few machine instructions in the most common cases. Our locks only require a partial word per object, and were implemented without increasing object size. We present measurements from our implementation in the JDK 1.1.2 for AIX, demonstrating speedups of up to a factor of 5 in micro-benchmarks and up to a factor of 1.7 in real programs.