Crossover from a pseudogap state to a superconducting state

On the basis of our calculation we deduce that the particular electronic structure of cuprate superconductors confines Cooper pairs to be firstly formed in the antinodal region which is far from the Fermi surface, and these pairs are incoherent and result in the pseudogap state. With the change of doping or temperature, some pairs are formed in the nodal region which locates the Fermi surface, and these pairs are coherent and lead to superconductivity. Thus the coexistence of the pseudogap and the superconducting gap is explained when the two kinds of gaps are not all on the Fermi surface. It is also shown that the symmetry of the pseudogap and the superconducting gap are determined by the electronic structure, and non-s wave symmetry gap favors the high-temperature superconductivity. Why the high-temperature superconductivity occurs in the metal region near the Mott metal-insulator transition is also explained.Comment: 7 pages, 2 figure

Modal Insan Dan Kependudukan Dalam Pembangunan Negara Menurut Ibn Khaldun

Human Capital and Demography In State Building in theThought of Ibn Khaldun. The career and thought of Ibn Khaldun has been an object of study for quite a long period of time, yet much aspects seem to be unceasinly attracting scholars' attention. The present article discusses Ibn Khaldun's view of human resource and its use in state development. The underlying argumentation of Ibn Khaldun's seems to be the importance of religion as the salient force of development. Any other natural or social forces-like the ashabiyyah and the natural suvival tendencies-by itself cannot be sufficient as the basis of civilized development

Competition between the BCS superconductivity and ferromagnetic spin fluctuations in MgCNi3_3

The low temperature specific heat of the superconductor MgCNi$_3$ and a non-superconductor MgC$_{0.85}$Ni$_3$ is investigated in detail. An additional contribution is observed from the data of MgCNi$_3$ but absent in MgC$_{0.85}$Ni$_3$, which is demonstrated to be insensitive to the applied magnetic field even up to 12 Tesla. A detailed discussion on its origin is then presented. By subtracting this additional contribution, the zero field specific heat of MgCNi$_3$ can be well described by the BCS theory with the gap ratio ($\Delta/k_BT_c$) determined by the previous tunneling measurements. The conventional s-wave pairing state is further proved by the magnetic field dependence of the specific heat at low temperatures and the behavior of the upper critical field.Comment: To appear in Physical Review B, 6 pages, 7 figure

Unsourced Random Massive Access with Beam-Space Tree Decoding

The core requirement of massive Machine-Type Communication (mMTC) is to support reliable and fast access for an enormous number of machine-type devices (MTDs). In many practical applications, the base station (BS) only concerns the list of received messages instead of the source information, introducing the emerging concept of unsourced random access (URA). Although some massive multiple-input multiple-output (MIMO) URA schemes have been proposed recently, the unique propagation properties of millimeter-wave (mmWave) massive MIMO systems are not fully exploited in conventional URA schemes. In grant-free random access, the BS cannot perform receive beamforming independently as the identities of active users are unknown to the BS. Therefore, only the intrinsic beam division property can be exploited to improve the decoding performance. In this paper, a URA scheme based on beam-space tree decoding is proposed for mmWave massive MIMO system. Specifically, two beam-space tree decoders are designed based on hard decision and soft decision, respectively, to utilize the beam division property. They both leverage the beam division property to assist in discriminating the sub-blocks transmitted from different users. Besides, the first decoder can reduce the searching space, enjoying a low complexity. The second decoder exploits the advantage of list decoding to recover the miss-detected packets. Simulation results verify the superiority of the proposed URA schemes compared to the conventional URA schemes in terms of error probability

Evidence for s-wave pairing from measurement on lower critical field in MgCNi3MgCNi_3

Magnetization measurements in the low field region have been carefully performed on a well-shaped cylindrical and an ellipsoidal sample of superconductor $MgCNi_3$. Data from both samples show almost the same results. The lower critical field $H_{c1}$ and the London penetration depth $\lambda$ are thus derived. It is found that the result of normalized superfluid density $\lambda^2(0)/\lambda^2(T)$ of $MgCNi_3$ can be well described by BCS prediction with the expectation for an isotropic s-wave superconductivity.Comment: To appear in Phys. Rev.

Nitrate in Groundwater and its Associated Health Risk: A Cross-Sectional Study in Mukim Salor, Kota Bharu, Kelantan, Malaysia

Background: Mukim Salor is an agricultural area in the district of Kota Bharu, Kelantan state, Malaysia. Farmers there use nitrogen-based fertilizers for paddy and vegetable planting. The use of these types of fertilizers may lead to contamination of nitrate in groundwater by the process of leaching into the soil. Kota Bharu is one of the areas in this country where the population still rely on groundwater as their main source of potable water. Daily use of water contaminated with nitrate may give rise to problems including “methe­moglobaenamia” or blue baby syndrome and shortness of breath. At the moment, there are no data available on nitrate levels or hazard index associated with nitrate exposure in groundwater in Mukim Salor. This study aimed to determine nitrate levels in groundwater and to perform health risk assessment from nitrate exposure among residents in Mukim Salor, a subdistrict in the district of Kota Bharu, Kelantan, an east coast state in Peninsular Malaysia. Subjects and Method: This cross-sectional study was conducted among residents from Mukim Salor, Kelantan, Malaysia. Fifty (50) respondents were chosen based on the inclusion and exclusion criteria and they were initially interviewed in order to obtain demographic data and groundwater usage information. Groundwater samples were taken from each of the respondent’s house who used groundwater exclusively for drinking and cooking. The samples were then analyzed using a HACH brand DR 1900 direct reading spectro­photometer. Risk assessment on exposure to nitrate was also calculated. Results: Nitrate levels ranged from 0.1 to 2.8 mg/L, with a mean of 1.08 + SD 0.64 mg/L. Nitrate levels in the area of study did not exceed the standard set by the health authorities (<10 mg/L) and there was no significant risk of nitrate contamination in ground water (where HI<1). Conclusion: Residents in Mukim Salor, Kelantan, Malaysia, were exposed to low levels of nitrate in groundwater. Keywords: Agriculture, nitrate, groundwater, methemoglobinaemia, health risk assessment, Mukim Salor

Correlations among superconductivity, structural instability, and band filling in Nb1-xB2 at the critical point x=0.2

We performed an extensive investigation on the correlations among superconductivity, structural instability and band filling in Nb1-xB2 materials. Structural measurements reveal that a notable phase transformation occurs at x=0.2, corresponding to the Fermi level (EF) in the pseudogap with the minimum total density of states (DOS) as demonstrated by the first-principles calculations. Superconductivity in Nb1-xB2 generally becomes visible in the Nb-deficient materials with x=0.2. Electron energy-loss spectroscopy (EELS) measurements on B K-edge directly demonstrated the presence of a chemical shift arising from the structural transformation. Our systematical experimental results in combination with theoretical analysis suggest that the emergence of hole states in the sigma-bands plays an important role for understanding the superconductivity and structural transition in Nb1-xB2.Comment: 16 pages, 4 figure