Southern Africa has experienced electric power deficits over the last decade. This has been due in part to the member countries＇ inadequate electrical power supply system, as well as load growth in areas which were n...Southern Africa has experienced electric power deficits over the last decade. This has been due in part to the member countries＇ inadequate electrical power supply system, as well as load growth in areas which were not adequately planned for. This has induced the formation of organizations such as SADC （Southern African Development Community） and SAPP （Southern African Power Pool） that have the common goal of achieving development and economic growth in the region which comprises of 15 member countries. This paper presents results from a security analysis of the region＇s electric power supply system using a baseline level of performance. This was carried out by performing a steady-state contingency analysis on a SADC power network model subject to the N-1 criteria which expresses the ability of the power network to experience a contingency without causing an overload or failure in any other part of the network. Simulations were carried out using DigSilent.展开更多
The radar power supplies exhibit a complex electronics. The development of more and more compact systems leads to master the interaction between different parts of the power supply while reducing electronic circuits, ...The radar power supplies exhibit a complex electronics. The development of more and more compact systems leads to master the interaction between different parts of the power supply while reducing electronic circuits, magnetic and thermal couplings from the constitutive circuitry. The consideration of these phenomena is very difficult at the design of the power supply. This paper presents two complementary methods based first on a circuitry model for the quantification of heat sources and secondly on finite element model for heat diffusion. This approach can help a designer in the goal of improving the performances and thermal stability of radar tied to the supply circuit subset.展开更多
The optimized geometries of the three complexes between MeH,~ （Me=Na, Mg, Be; n=1 or 2） and Sill4 have been calculated at the B3LYP/6-31 1＋＋g＊＊, MP2/6-31 1＋＋g（3df,3pd） and MP2/aug-cc-pvtz levels, respectivel...The optimized geometries of the three complexes between MeH,~ （Me=Na, Mg, Be; n=1 or 2） and Sill4 have been calculated at the B3LYP/6-31 1＋＋g＊＊, MP2/6-31 1＋＋g（3df,3pd） and MP2/aug-cc-pvtz levels, respectively. The red-shift inverse hydrogen bonds （IHBs） based on Si-H, an electron donor, were reported. The calculated binding energies with basis set super-position error （BSSE） correction of the three complexes are -5.98, -8.65 and -3.96 kJ mol^-1 （MP2/6-311＋＋g（3df, 3pd））, respectively, which agree with the results obtained via MP2/aug-cc-pvtz （-6.18, -9.12 and -4.28 kJ mol^-1, respectively）. The relative stabilities of the three complexes are in the order of SiH4...MgH2 〉 SiH4...NaH 〉 SiH4...BeH2. Natural bond orbital theory （NBO） analysis and the chemical shift calculation of the related atoms revealed that the charges flow from Sill4 to MeHn and the chemical shifts of the interacting H shift to downfield. Here, the Sil-H3 of Sill4 acts as both a bond hydrogen donor and an electron donor. Therefore, compared with conventional hydrogen bonds, they formed IHB complexes. Atoms in molecules （AIM） theory have been used to investigate the topological properties of the critical points in the three IHB structures.展开更多
Suppose Mi = Vi ∪ Wi （i = 1,2） are Heegaard splittings. A homeomorphism f ： F1 → F2 produces an attached manifold M = M1 ∪F1=F2 M2, where Fi ∪→ δ_Wi. In this paper we define a surface sum of Heegaard splittin...Suppose Mi = Vi ∪ Wi （i = 1,2） are Heegaard splittings. A homeomorphism f ： F1 → F2 produces an attached manifold M = M1 ∪F1=F2 M2, where Fi ∪→ δ_Wi. In this paper we define a surface sum of Heegaard splittings induced from the Heegaard splittings of M1 and M2, and give a sufficient condition when the surface sum of Heegaard splitting is stabilized. We also give examples showing that the surface sum of Heegaard splittings can be unstabilized. This indicates that the surface sum of Heegaard splittings and the amalgamation of Heegaard splittings can give different Heegaard structures.展开更多
文摘Southern Africa has experienced electric power deficits over the last decade. This has been due in part to the member countries＇ inadequate electrical power supply system, as well as load growth in areas which were not adequately planned for. This has induced the formation of organizations such as SADC （Southern African Development Community） and SAPP （Southern African Power Pool） that have the common goal of achieving development and economic growth in the region which comprises of 15 member countries. This paper presents results from a security analysis of the region＇s electric power supply system using a baseline level of performance. This was carried out by performing a steady-state contingency analysis on a SADC power network model subject to the N-1 criteria which expresses the ability of the power network to experience a contingency without causing an overload or failure in any other part of the network. Simulations were carried out using DigSilent.
文摘The radar power supplies exhibit a complex electronics. The development of more and more compact systems leads to master the interaction between different parts of the power supply while reducing electronic circuits, magnetic and thermal couplings from the constitutive circuitry. The consideration of these phenomena is very difficult at the design of the power supply. This paper presents two complementary methods based first on a circuitry model for the quantification of heat sources and secondly on finite element model for heat diffusion. This approach can help a designer in the goal of improving the performances and thermal stability of radar tied to the supply circuit subset.
基金supported by the National Natural Science Foundation of China (50975273)the "QingLan" Talent Engineering Funds of Tianshui Normal University
文摘The optimized geometries of the three complexes between MeH,~ （Me=Na, Mg, Be; n=1 or 2） and Sill4 have been calculated at the B3LYP/6-31 1＋＋g＊＊, MP2/6-31 1＋＋g（3df,3pd） and MP2/aug-cc-pvtz levels, respectively. The red-shift inverse hydrogen bonds （IHBs） based on Si-H, an electron donor, were reported. The calculated binding energies with basis set super-position error （BSSE） correction of the three complexes are -5.98, -8.65 and -3.96 kJ mol^-1 （MP2/6-311＋＋g（3df, 3pd））, respectively, which agree with the results obtained via MP2/aug-cc-pvtz （-6.18, -9.12 and -4.28 kJ mol^-1, respectively）. The relative stabilities of the three complexes are in the order of SiH4...MgH2 〉 SiH4...NaH 〉 SiH4...BeH2. Natural bond orbital theory （NBO） analysis and the chemical shift calculation of the related atoms revealed that the charges flow from Sill4 to MeHn and the chemical shifts of the interacting H shift to downfield. Here, the Sil-H3 of Sill4 acts as both a bond hydrogen donor and an electron donor. Therefore, compared with conventional hydrogen bonds, they formed IHB complexes. Atoms in molecules （AIM） theory have been used to investigate the topological properties of the critical points in the three IHB structures.
基金the Specialized Research Fund for the Doctoral Program of Higher Education(No.200801411069)
文摘Suppose Mi = Vi ∪ Wi （i = 1,2） are Heegaard splittings. A homeomorphism f ： F1 → F2 produces an attached manifold M = M1 ∪F1=F2 M2, where Fi ∪→ δ_Wi. In this paper we define a surface sum of Heegaard splittings induced from the Heegaard splittings of M1 and M2, and give a sufficient condition when the surface sum of Heegaard splitting is stabilized. We also give examples showing that the surface sum of Heegaard splittings can be unstabilized. This indicates that the surface sum of Heegaard splittings and the amalgamation of Heegaard splittings can give different Heegaard structures.
