Hydrogen Storage Properties of the Tetrahydrofuran Treated Magnesium

The electronic structure, crystalline feature and morphology of the tetrahydrofuran (THF) treated magnesium, along with its hydriding and dehydriding properties have been investigated. The THF treated magnesium absorbs 6.3 wt per cent hydrogen at 723K and 3.5 MPa. After hydrogenation, in addition to the expected MgH2, a new less-stable hydride phase appears at 673K, but not at a lower temperature. Desorption produces 5.5 wt per cent hydrogen at 723K against a back pressure of 1.3 Pa after 20 cycles of hydriding-dehydriding. The THF treatment improves the kinetics of hydrogen absorption and desorption significantly. From 723K to 623K, the THF treated Mg demonstrates acceptable reaction rates. XPS studies show that tetrahydrofuran treatment causes the electronic energy state of the magnesium surface atoms to change, but the XRD studies show the crystal structure remains unchanged. Metallographic observation of the bulk hydrides of THF treated magnesium reveal they are poly-crystalline wi th the wide-spreading slip bands and twins within the crystals, indicating the phase transformation upon hydriding causes serious stress and distortion. It appears this microstructural deformation explains the much higher energy requirements (higher pressure and temperature) for magnesium hydrogenation than the simple lattice expansion that accompany hydrogen uptake for LaNi5 and FeTi

From burstiness characterisation to traffic control strategy : a unified approach to integrated broadbank networks

The major challenge in the design of an integrated network is the integration and support of a wide variety of applications. To provide the requested performance guarantees, a traffic control strategy has to allocate network resources according to the characteristics of input traffic. Specifically, the definition of traffic characterisation is significant in network conception. In this thesis, a traffic stream is characterised based on a virtual queue principle. This approach provides the necessary link between network resources allocation and traffic control. It is difficult to guarantee performance without prior knowledge of the worst behaviour in statistical multiplexing. Accordingly, we investigate the worst case scenarios in a statistical multiplexer. We evaluate the upper bounds on the probabilities of buffer overflow in a multiplexer, and data loss of an input stream. It is found that in networks without traffic control, simply controlling the utilisation of a multiplexer does not improve the ability to guarantee performance. Instead, the availability of buffer capacity and the degree of correlation among the input traffic dominate the effect on the performance of loss. The leaky bucket mechanism has been proposed to prevent ATM networks from performance degradation due to congestion. We study the leaky bucket mechanism as a regulation element that protects an input stream. We evaluate the optimal parameter settings and analyse the worst case performance. To investigate its effectiveness, we analyse the delay performance of a leaky bucket regulated multiplexer. Numerical results show that the leaky bucket mechanism can provide well-behaved traffic with guaranteed delay bound in the presence of misbehaving traffic. Using the leaky bucket mechanism, a general strategy based on burstiness characterisation, called the LB-Dynamic policy, is developed for packet scheduling. This traffic control strategy is closely related to the allocation of both bandwidth and buffer in each switching node. In addition, the LB-Dynamic policy monitors the allocated network resources and guarantees the network performance of each established connection, irrespective of the traffic intensity and arrival patterns of incoming packets. Simulation studies demonstrate that the LB-Dynamic policy is able to provide the requested service quality for heterogeneous traffic in integrated broadband networks

Jonah's Prayer: a Composition for Solo Tenor, Mixed Chorus and Two Pianos

Jonah's Prayer is a choral work for solo tenor, a mixed choir of not fewer than 30 members, two pianos and a few percussion instruments to be played by choir members. The piece lasts about 13 minutes; it is a work intended for church choir use but could be performed in other venues as well

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Department of ComputingRefereed conference pape

Stability and Reversibility of Lithium Borohydrides Doped by Metal Halides and Hydrides

In an effort to develop reversible metal borohydrides with high hydrogen storage capacities and low dehydriding temperature, doping LiBH4 with various metal halides and hydrides has been conducted. Several metal halides such as TiCl3, TiF3, and ZnF2 effectively reduced the dehydriding temperature through a cation exchange interaction. Some of the halide doped LiBH4 are partially reversible. The LiBH4 + 0.1TiF3 desorbed 3.5 wt % and 8.5 wt % hydrogen at 150 and 450 °C, respectively, with subsequent reabsorption of 6 wt % hydrogen at 500 °C and 70 bar observed. XRD and NMR analysis of the rehydrided samples confirmed the reformation of LiBH4. The existence of the (B12H12)−2 species in dehydrided and rehydrided samples gives insight into the resultant partial reversibility. A number of other halides, MgF2, MgCl2, CaCl2, SrCl2, and FeCl3, did not reduce the dehydriding temperature of LiBH4 significantly. XRD and TGA-RGA analyses indicated that an increasing proportion of halides such as TiCl3, TiF3, and ZnCl2 from 0.1 to 0.5 mol makes lithium borohydrides less stable and volatile. Although the less stable borohydrides such as LiBH4 + 0.5TiCl3, LiBH4 + 0.5TiF3, and LiBH4 + 0.5ZnCl2 release hydrogen at room temperature, they are not reversible due to unrecoverable boron loss caused by diborane emission. In most cases, doping that produced less stable borohydrides also reduced the reversible hydrogen uptake. It was also observed that halide doping changed the melting points and reduced air sensitivity of lithium borohydrides

Structural Identity-Based Encryption

In this paper, we introduce the concept of structural identity-based encryption (SIBE). Similar to hierarchical identity-based encryption (HIBE), entities in the system are organized into hierarchy. An entity in SIBE can decrypt ciphertext for all its ancestors. It can be seen as an opposite of HIBE, where an entity can decrypt the ciphertext for all its descendants. We formalize the notion and security requirements, propose an efficient construction and show that our construction is secure under appropriate assumptions in the random oracle model

A report on an exploratory study on visual conditions of older people living in public housing

HOPE worldwide (HWW) has been a chartered charity organization in Hong Kong since 1993, with its focus on organizing service programmes in China and Hong Kong. Volunteers for Seniors Day (formerly Hope for Seniors Day) is one of the many programmes initiated by HWW to meet the urgent needs of the growing ageing population in Hong Kong. Starting in 1996, volunteers from corporations and social organizations have been recruited for Volunteers for Seniors Days on an annual basis. Since 2000, the programme has been jointly organized with the Housing Authority to provide cleaning and painting services to single elderly tenants living in public housing estates. It also helps to build relationships between the volunteers and the elderly people in the community. Over the past nine years, the programme has served over 5,300 single elderly people and mobilized more than 20,000 volunteers to participate. In the survey conducted by HWW during Volunteers for Seniors Day 2004, we found that there were up to 40.1% and 49.6% of the single elderly living in public housing estates suffering from various kinds of eye diseases and poor eyesight respectively. The prevalence of eye diseases and poor eyesight would result in a high percentage of falls and thereby affect their functional activities of daily living (ADL). In fact, most of the eye diseases are curable with early detection and treatment, and elderly people with poor eyesight may need minor home adaptation e.g. handrails or night lights to prevent home accidents. According to a study by the Department of Orthopaedics & Traumatology of Chinese University, exercise is important to the elderly and can strengthen their low-limb and upper-limb muscles, which in turn prevents falls at home or on the street. Due to the above findings, HWW cooperated with Housing Authority to initiate a pilot programme to help identify the eye diseases as well as provide public health education to the elderly in 30 public estates in the second half of 2004. Health care professionals provided training to 150 volunteers on eye care knowledge and simple eye screening tests that could be carried out in road shows in shopping arcades of public housing estates. In addition, experienced ophthalmologists or optometrists were present to answer elderly participants’ inquiries on eye health and delivered health information during the kick-off ceremony and road shows in the shopping arcades. The programme had the following objectives: To enhance the awareness of eye health and eye diseases of the elderly through 30 public eye screenings at public housing arcades; To carry out a survey on the visual conditions of elderly living in public housing; and To foster partnership between government, NGO and business sectors in promoting the health of the elderly in the community

GABAergic synaptic scaling is triggered by changes in spiking activity rather than transmitter receptor activation

Homeostatic plasticity represents a set of mechanisms that are thought to recover some aspect of neural function. One such mechanism called AMPAergic scaling was thought to be a likely candidate to homeostatically control spiking activity. However, recent findings have forced us to reconsider this idea as several studies suggest AMPAergic scaling is not directly triggered by changes in spiking. Moreover, studies examining homeostatic perturbations in vivo have suggested that GABAergic synapses may be more critical in terms of spiking homeostasis. Here we show results that GABAergic scaling can act to homeostatically control spiking levels. We find that increased or decreased spiking in cortical cultures triggers multiplicative GABAergic upscaling and downscaling, respectively. In contrast, we find that changes in AMPAR or GABAR transmission only influence GABAergic scaling through their indirect effect on spiking. We propose that GABAergic scaling, rather than glutamatergic scaling, is a key player in spike rate homeostasis