Country-level impact of global recession and China’s stimulus package

A dynamic computable general equilibrium model is developed to assess the impact of the recent global recession and the Chinese government’s stimulus package on China’s economic growth. The model is first used to capture the actual sector-level economic growth in 2008 and the possible economic performance in 2009 without the intervention of the Chinese government through its stimulus package. Under this global recession scenario, the GDP growth rate in 2009 falls to 2.9 percent mainly as a result of the sharp drop in exports of manufactured goods, while the agricultural sector is more crisis-resilient. Because export-oriented manufacturing sectors are often import-intensive, the weakened economy is accompanied by a reduction in Chinese firms’ import demand for materials, intermediates, and capital goods. The model also shows that without government intervention, the negative effect of a one-year shock on the Chinese economy would last for many years. Also, over the next five to six years, China is unlikely to replicate its strong economic performance of the past two decades. China’s stimulus package is modeled through increased investment financed by government resources. With additional demand on investment goods, growth in the investment-related production sector is stimulated. Through the cross-sector linkages in a general equilibrium model, the demand for other noncapital goods increases, thus stimulating growth in these sectors. As production of more industrialized sectors starts to grow, so will households’ income and consumption, providing market opportunities for those agricultural and service sectors that mainly produce for the domestic market. Under the stimulus scenario, the Chinese economy is expected to grow 8–10 percent in 2009 and the succeeding years. The growth engine in this case differs from that before 2008: growth is led by domestic demand, while trade still falls significantly in 2009 (instead of the double-digit growth before 2008). Domestic demand-driven stimulus growth creates jobs, and hence it increases income for both urban and rural households. The model is also used to measure the overall gains of the stimulus package by comparing GDP between the two scenarios. Without considering the productivity-enhancing role of public investment as part of the stimulus package (which is important for long-term growth but unlikely to happen in the short run), the cumulative difference of the GDP between the two scenarios over the next seven years is about RMB76 trillion, which is about three times more than the GDP in 2007.China stimulus package, Development strategies, general equilibrium modeling, global financial crisis,

Fading-aware packet scheduling algorithm in OFDM-MIMO systems

To maximize system throughput and guarantee the quality of service(QoS) of multimedia traffic in orthogonal frequency division multiplexing(OFDM) systems with smart antennas, a new packet scheduler is introduced to consider QoS requirements, packet location in the frame, and modulation level. In the frequency domain, several consecutive subchannels are grouped as a frequency subband. Each subband in a frame can be used to transmit a packet, and can be reused by several users in a multiple-input and multiple-output (MIMO) systems. In this paper, we consider the adaptive packet scheduling algorithms design for OFDM/SDMA system.Based on the BER requirements, all traffics are divided into classes.Based on such classification, a dynamic packet scheduler is proposed,which greatly improves system capacity, and can guarantee QoS requirements.Adaptive modulation is also applied in the scheduler. Then, the complexity analysis of these algorithms is given. When compared with existing schedulers, our scheduler achieves higher system capacity with much reduced complexity. The use of adaptive modulation further enhances the system capacity. Simulation results demonstrate that as the traffic load increases, the new scheduler has much better performance in system throughput, average delay, and packet loss rate.published_or_final_versio

Medium access control with physical-layer-assisted link differentiation

In this paper, we develop medium access control (MAC) schemes for both contention and contention-free accesses over wireless local area networks and give performance analysis of these MAC protocols. User detection and multirate adaptation (MRA) modules are proposed in the physical layer (PHY) to assist link differentiation. With these two modules, for contention accesses, a new distributed queuing MAC protocol (PALD-DQMP) is proposed. Based on different users' channel states, PALD-DQMP makes use of a distributed queuing system to schedule transmissions. To support multimedia transmissions, an enhanced PALD-DQMP (E-PALD-DQMP) is designed by providing two-level optimized transmission scheduling for four access categories, thus eliminating both external and internal collisions among mobile stations. For contention-free accesses, based on the same PHY-assisted link differentiation provided by the two modules, a new multipolling MAC protocol (PALD-MPMP) is proposed, which not only reduces the polling overhead but also prioritizes transmissions according to their delay requirements. Performance analysis and simulation results show that our proposed protocols outperform the standard MAC protocols for both delay-sensitive and best-effort traffics. All these improvements are mainly attributed to the awareness of cross-layer channel state information and the consequent MRA scheme. © 2008 IEEE.published_or_final_versio

Applicability and failure of the flux-gradient laws in double-diffusive convection

The article of record as published may be found at http://dx.doi.org/10.1017/jfm.2014.244Double-diffusive flux-gradient laws are commonly used to describe the development of large-scale structures driven by salt fingers – thermohaline staircases, collective instability waves and intrusions. The flux-gradient model assumes that the vertical transport is uniquely determined by the local background temperature and salinity gradients. While flux-gradient laws adequately capture mixing characteristics on scales that greatly exceed those of primary double-diffusive instabilities, their accuracy rapidly deteriorates when the scale separation between primary and secondary instabilities is reduced. This study examines conditions for the breakdown of the flux-gradient laws using a combination of analytical arguments and direct numerical simulations. The applicability (failure) of the flux-gradient laws at large (small) scales is illustrated through the example of layering instability, which results in the spontaneous formation of thermohaline staircases from uniform temperature and salinity gradients. Our inquiry is focused on the properties of the ‘point-of-failure’ scale (Hpof ) at which the vertical transport becomes significantly affected by the non-uniformity of the background stratification. It is hypothesized that Hpof can control some key characteristics of secondary double-diffusive phenomena, such as the thickness of high-gradient interfaces in thermohaline staircases. A more general parametrization of the vertical transport – the flux-gradient-aberrancy law – is proposed, which includes the selective damping of relatively short wavelengths that are inadequately represented by the flux-gradient models. The new formulation is free from the unphysical behaviour of the flux-gradient laws at small scales (e.g. the ultraviolet catastrophe) and can be readily implemented in theoretical and large-scale numerical models of double-diffusive convection

CPLD-PGPS scheduling algorithm in wireless OFDM systems

In this paper, we propose a new scheduler for orthogonal frequency-division multiplexing (OFDM) wireless communication systems, called Channel-Condition and Packet-Length Dependent Packet Generalized Processor Sharing (CPLD-PGPS) scheduler. CPLD scheduler considers the condition of the physical channel and the length of packets at the same time, and optimally allocates the sub-carriers in a frame. With this scheduler, the system can achieve better system BER performance, and correspondingly superior PER performance. The system throughput is improved, at the same time the required bandwidth is guaranteed, and long term fairness for all the traffic in the system is provided. In order to reduce the algorithm complexity, a simplified CPLD is proposed, which maintains the system throughput as in the original scheduler, and guarantees the system performance with properly set system parameters. The superior performance of the proposed scheduler is demonstrated by simulation results. © 2004 IEEE.published_or_final_versio

Multiobjective optimized bipartite matching for resource allocation

The Hungarian algorithm can provide the maximum weighted bipartite matching for assignment problems. However it can only solve the single objective weight optimization problem. In this paper, a modified bipartite matching (MBM) algorithm is proposed to solve the weighted bipartite matching problem with multiobjective optimization. In addition, our MBM algorithm is applicable to asymmetric bipartite graph, which is common in resource allocation problems. We illustrate the application of MBM to antenna assignments in wireless multipleinput multiple-output (MIMO) systems for both symmetric and asymmetric scenarios. The simulation results show that MBM enjoys low computational complexity and maximizes the system capacity, while keeping the fairness among mobile users. © 2007 IEEE.published_or_final_versio

A channel-condition and packet-length dependent scheduler in wireless OFDM systems

In this paper, a new scheduler, called Channel-Condition and Packet-Length Dependent Packet Generalized Processor Sharing (CPLD-PGPS) scheduler is proposed for orthogonal frequency-division multiplexing (OFDM) wireless communication systems. Based on PGPS, CPLD scheduler considers the condition of the physical channel and the length of packets at the same time, and optimally allocates the sub-carriers in a frame. With this scheduler, improved system BER, and correspondingly superior PER performance can be achieved. The system throughput is improved, while guaranteeing the required bandwidth, and providing long term fairness for all the traffic in the system. In order to reduce the algorithm complexity, a simplified CPLD is proposed, which maintains the system throughput as the original scheduler, and guarantees the system performance with properly set system parameters. Simulation results demonstrate the superior performance of the proposed scheduler. © 2004 IEEE.published_or_final_versio

CPLD-PGPS scheduler in wireless OFDM systems

In this paper, we propose a new scheduler for orthogonal frequency-division multiplexing (OFDM) wireless communication systems, called Channel-Condition and Packet-Length Dependent Packet Generalized Processor Sharing (CPLD-PGPS) scheduler. Based on PGPS, the CPLD scheduler considers both the physical channel condition and the length of packets, and optimally allocates the sub-carriers to different users. The total transmit power is adaptively allocated to each subcarrier. With this scheduler, the system can achieve better system BER performance, and correspondingly superior PER performance. The system throughput is improved, the required bandwidth is guaranteed, and long term fairness for all traffic in the system is provided. In order to reduce the complexity, a simplified algorithm is proposed, which maintains the system throughput as in the original scheduler, and guarantees the system performance with properly set system parameters. The superior performance of the proposed schedulers is demonstrated by simulation with multimedia traffic. © 2006 IEEE.published_or_final_versio

Specific Surface Areas of Porous Cu Manufactured by Lost Carbonate Sintering: Measurements by Quantitative Stereology and Cyclic Voltammetry

Open-cell porous metals have many applications due to high surface area to volume ratios. Porous metals manufactured by the space holder methods have distinctively different porous structure from commercial open-cell metal foams, but very little research has been conducted to characterise the surface area of this class of materials. This paper measured the geometric, electroactive and real surface areas of porous Cu samples manufactured by the Lost Carbonate Sintering process by quantitative stereology and cyclic voltammetry. A cyclic voltammetry (peak current) procedure has been developed and successfully applied to the measurement of electroactive surface areas of the porous Cu. For porous Cu samples with pore sizes 75-1500 µm and porosities 0.5-0.8, the volumetric and gravimetric specific geometric, electroactive and real surface areas are in the ranges of 15-90 cm-1 and 5-45 cm2/g, 200-400 cm-1 and 40-130 cm2/g, and 1000-2500 cm-1 and 400-800 cm2/g, respectively, varying with pore size and porosity. The geometric, electroactive and real surface areas are found to result from the contributions from primary porosity, primary and secondary porosities, and surfaces of metal particles, respectively. The measurement methods adopted in this study can provide vital information of surface areas at different length scales, which is important for many applications