Competition between structural distortion and magnetic moment formation in fullerene C20_{20}

We investigated the effect of on-site Coulomb interactions on the structural and magnetic ground state of the fullerene C$_{20}$ based on density-functional-theory calculations within the local density approximation plus on-site Coulomb corrections (LDA+$U$). The total energies of the high symmetry ($I_{h}$) and distorted ($D_{3d}$) structures of C$_{20}$ were calculated for different spin configurations. The ground state configurations were found to depend on the forms of exchange-correlation potentials and the on-site Coulomb interaction parameter $U$, reflecting the subtle nature of the competition between Jahn-Teller distortion and magnetic instability in fullerene C$_{20}$. While the non-magnetic state of the distorted $D_{3d}$ structure is robust for small $U$, a magnetic ground state of the undistorted $I_{h}$ structure emerges for $U$ larger than 4 eV when the LDA exchange-correlation potential is employed.Comment: 4 figures, 1 tabl

Noise Source Identification of Small Fan-BLDC Motor System for Refrigerators

Noise levels in household appliances are increasingly attracting attention from manufacturers and customers. Legislation is becoming more severe on acceptable noise levels and low noise is a major marketing point for many products. The latest trend in the refrigerator manufacturing industry is to use brushless DC (BLDC) motors instead of induction motors in order to reduce energy consumption and noise radiation. However, cogging torque from BLDC motor is an undesirable effect that prevents the smooth rotation of the rotor and results in noise. This paper presents a practical approach for identifying the source of excessive noise in the small fan-motor system for household refrigerators. The source is presumed to a mechanical resonance excited by torque ripple of the BLDC motor. By using finite element analysis, natural frequencies and mode shapes of the rotating part of the system are obtained and they are compared with experimental mode shapes obtained by electronic torsional excitation test which uses BLDC motor itself as an exciter. Two experimental validations are carried out to confirm the reduction of excessive noise

Guards and Culprits in the Endoplasmic Reticulum: Glucolipotoxicity and β-Cell Failure in Type II Diabetes

The endoplasmic reticulum (ER) is a cellular organelle responsible for multiple important cellular functions including the biosynthesis and folding of newly synthesized proteins destined for secretion, such as insulin. The ER participates in all branches of metabolism, linking nutrient sensing to cellular signaling. Many pathological and physiological factors perturb ER function and induce ER stress. ER stress triggers an adaptive signaling cascade, called the unfolded protein response (UPR), to relieve the stress. The failure of the UPR to resolve ER stress leads to pathological conditions such as β-cell dysfunction and death, and type II diabetes. However, much less is known about the fine details of the control and regulation of the ER response to hyperglycemia (glucotoxicity), hyperlipidemia (lipotoxicity), and the combination of both (glucolipotoxicity). This paper considers recent insights into how the response is regulated, which may provide clues into the mechanism of ER stress-mediated β-cell dysfunction and death during the progression of glucolipotoxicity-induced type II diabetes