Vacuum induced Berry phases in single-mode Jaynes-Cummings models

Motivated by the work [Phys. Rev. Lett. 89, 220404 (2002)] for detecting the vacuum-induced Berry phases with two-mode Jaynes-Cummings models (JCMs), we show here that, for a parameter-dependent single-mode JCM, certain atom-field states also acquire the photon-number-dependent Berry phases after the parameter slowly changed and eventually returned to its initial value. This geometric effect related to the field quantization still exists, even the filed is kept in its vacuum state. Specifically, a feasible Ramsey interference experiment with cavity quantum electrodynamics (QED) system is designed to detect the vacuum-induced Berry phase.Comment: 10 pages, 4 figures

Glauber-based evaluations of the odd moments of the initial eccentricity relative to the even order participant planes

Monte Carlo simulations are used to compute the centrality dependence of the odd moments of the initial eccentricity $\epsilon_{n+1}$, relative to the even order (n) participant planes $\Psi^*_n$ in Au+Au collisions. The results obtained for two models of the eccentricity -- the Glauber and the factorized Kharzeev-Levin-Nardi (fKLN) models -- indicate magnitudes which are essentially zero. They suggest that a possible correlation between the orientations of the the odd and even participant planes ($\Psi^*_{n+1}$ and $\Psi^*_n$ respectively), do not have a significant influence on the calculated eccentricities. An experimental verification test for correlations between the orientations of the the odd and even participant planes is also proposed.Comment: 3 pages, 1 figure. Version accepted for publicatio

Optimal chiller loading in dual-temperature chilled water plants for energy saving

Buildings account for almost 40% of global energy consumption. Due to the high energy consumption of chilled water plants, various studies have optimized chiller loading in plants with multiple chillers for energy conservation. However, few studies have optimized dual-temperature chiller plants, even though better energy efficiency could be achieved than that of typical single-temperature chiller plants. This paper proposes two optimal control strategies for dual-temperature chilled water plants, strategy B and strategy C. Strategy B optimizes the cooling load distribution of the chillers in each group by adjusting the cooling load ratio of each chiller. Under this strategy, the energy consumption of the chiller plant for the entire cooling season was reduced by 10.1%. Meanwhile, strategy C optimizes the cooling load distribution among chillers in the same chiller group and between two chiller groups, by simultaneously adjusting the temperature setpoint of the air leaving the primary cooling coils and the partial load ratio of each chiller. By considering both the impact of the chilled water loop and the air handling process, strategy C achieved greater energy saving (16.4%) for the entire cooling season. In hot summer months, the energy savings arise mainly from optimization of the cooling load distribution among chillers in each chiller group, as this optimization accounts for 63–68% of the total savings. In moderate months, optimizing the cooling load distribution among chillers in the same group and optimizing the distribution between two chiller groups account for nearly the same proportion of the total energy savings

A review of optimization approaches for controlling water-cooled central cooling systems

Buildings consume a large amount of energy across all sectors of society, and a large proportion of building energy is used by HVAC systems to provide a comfortable and healthy indoor environment. In medium and large-size buildings, the central cooling system accounts for a major share of the energy consumption of the HVAC system. Improving the cooling system efficiency has gained much attention as the reduction of cooling system energy use can effectively contribute to environmental sustainability. The control and operation play an important role in central cooling system energy efficiency under dynamic working conditions. It has been proven that optimization of the control of the central cooling system can notably reduce the energy consumption of the system and mitigate greenhouse gas emissions. In recent years, numerous studies focus on this topic to improve the performance of optimal control in different aspects (e.g., energy efficiency, stability, robustness, and computation efficiency). This paper provides an up-to-date overview of the research and development of optimization approaches for controlling water-cooled central cooling systems, helping readers to understand the new significant trends and achievements in this area. The optimization approaches have been classified as system-model-based and data-based. In this paper, the optimization methodology is introduced first by summarizing the key decision variables, objective function, constraints, and optimization algorithms. The principle and performance of various optimization approaches are then summarized and compared according to their classification. Finally, the challenges and development trends for optimal control of water-cooled central cooling systems are discussed

Study on the performance of two water-side free cooling methods in a semiconductor manufacturing factory

Buildings account for a large portion of global energy consumption and CO2 emissions. Therefore, reducing the energy demands of buildings has become a global topic for sustainable development. A central cooling system accounts for a significant part of a building’s energy consumption. This study proposes a tap water-based free cooling system that recovers heat from spaces for tap water preheating in winter. The tap water-based free cooling and cooling tower free cooling systems integrated with a water-cooled central cooling system were applied in a semiconductor manufacturing factory. Based on the whole-year operation data, the performance of the tap water-based free cooling and cooling tower free cooling systems were compared from thermodynamic, energy, environmental, and economic perspectives. The results showed that free cooling was the dominant cooling method in winter in Tianjin. Compared with the cooling tower free cooling system, the tap water-based free cooling system could provide slightly higher chilled water temperature resulting in 10% shorter operating time. The energy analysis revealed that the coefficient of performance (COP) of the tap water-based free cooling system was approximately 7.4-fold and 2.2-fold higher than that of the mechanical cooling and cooling tower free cooling systems, respectively. Using the two free cooling methods reduced electricity consumption by 6,044 MWh and reached an annual energy-saving rate of 15.1%. Furthermore, the tap water-based free cooling system saved 1.48×105 kg of natural gas for tap water preheating. Energy reductions attributed to two free cooling methods reduced CO2 emissions by 6,236 tons. The tap water-based free cooling is more environmentally friendly with a 4.4-fold greater CO2 emission reduction rate than the cooling tower free cooling method. From the economic perspective, with a short payback period (1.4 years), the tap water-based free cooling system is an attractive solution for improving the energy efficiency of central cooling systems

Environmental damage costs from airborne pollution in the major cities in China

This paper estimates the environment external costs due to air pollutants via the impacts pathway approach used for ExternE project in the major cities in China over the period 2003-2006. The estimation results show that the external costs were US$ 20.15 billion in 2006, representing 2.28% of gross domestic product (GDP). This means that China suffered a lot for the air pollutants with the development of the economy. In the composition of external costs, damages to human health are the effects that generate the major part of externalities associated with air pollutants in these cities. The trend of external costs representing GDP in the sum of major cities was declining from 2003 to 2006, though the group in risk and agricultural products was increasing. Based on these finding, effective environmental policies and plans for economic development in these cities should focus not only on the volume of pollutants emission of SO2 and PM10, but also take other impact factors into account

Pickup velocity of nanoparticles

This paper represents the first systematic study of the pneumatic conveying of nanoparticles. The minimum pickup velocity, Upu, of six nanoparticle species of different materials (i.e., silicon dioxide (SiO2), aluminum oxide (Al2O3) and titanium dioxide (TiO2)) and surfaces (i.e., apolar and polar) were determined by the weight loss method. Specifically, the weight loss method involves measuring the mass loss from the particle sample at various superficial gas velocities (U), and the Upu is the U value at which mass loss is zero. Nanoparticles were picked up as agglomerates rather than individually. Results show that (a) due to relative lack of hydrogen bonding, apolar nanoparticles have higher mass loss values at the same velocities, mass loss curves with accentuated S-shaped profiles, and lower Upu values; (b) among the three species, SiO2, which has the lowest Hamaker coefficient, exhibited the greatest discrepancy between apolar and polar surfaces with respect to both mass loss curves and Upu values; (c) Umf,polar/Umf,apolar was between 1 – 3.5 times that of Upu,polar/Upu,apolar due to greater extents of hydrogen bonding associated with Umf ; (d) Upu values are at least an order-of-magnitude lower than that expected from the well-acknowledged Upu correlation (1) due to agglomeration; (e) although nanoparticles should be categorized as Zone III (1) (or Geldart Group C (2)), the nanoparticles, and primary and complex agglomerates agree more with the Zone I (or Geldart Group B) correlation (Figure 1, whereby Rep* and Ar are the particle Reynolds number and Archimedes number, respectively (1)). In view of the importance of surface polarity on the pneumatic conveying of nanoparticles, more studies are on-going to further understand such surface effects. Please click Additional Files below to see the full abstract