Ambient pressure colossal magnetocaloric effect tuned by composition in Mn(1-x)Fe(x)As.

The magnetocaloric effect (MCE) is the basis for magnetic refrigeration, and can replace conventional gas compression technology due to its superior efficiency and environment friendliness. MCE materials must exhibit a large temperature variation in response to an adiabatic magnetic-field variation and a large isothermal entropic effect is also expected. In this respect, MnAs shows the colossal MCE, but the effect appears under high pressures. In this work, we report on the properties of Mn(1-x)Fe(x)As that exhibit the colossal effect at ambient pressure. The MCE peak varies from 285 K to 310 K depending on the Fe concentration. Although a large thermal hysteresis is observed, the colossal effect at ambient pressure brings layered magnetic regenerators with huge refrigerating power closer to practical applications around room temperature.

Pressure-induced colossal magnetocaloric effect in MnAs.

To present day, the maximum magnetocaloric effect (MCE) at room temperature for a magnetic field change of 5 T is 40 J/(kg K) for MnAs. In this Letter we present colossal MCE measurements on MnAs under pressure, reaching values up to 267 J/(kg K), far greater than the magnetic limit arising from the assumption of magnetic field independence of the lattice and electronic entropy contributions. The origin of the effect is the contribution to the entropy variation coming from the lattice through the magnetoelastic coupling.

Intra-His bundle block. Clinical, electrocardiographic, and electrophysiologic characteristics.

OBJECTIVE: To assess the clinical, electrocardiographic, and electrophysiologic characteristics of patients (pt) with intra-His bundle block undergoing an electrophysiologic study (EPS). METHODS: We analyzed the characteristics of 16 pt with second-degree atrioventricular block and symptoms of syncope or dyspnea, or both, undergoing conventional EPS. RESULTS: Intra-His bundle block was documented in 16 pt during an EPS. In 15 (94%) pt, the atrioventricular block was recorded in sinus rhythm; 4 (25%) pt had intra-His Wenckebach phenomenon, which correlated with Mobitz I (MI) atrioventricular block on the electrocardiogram. Seven (44%) pt had 2:1 atrioventricular block, 2 of whom were asymptomatic (12.5%). One (6%) pt had intra- and infra-His bundle block. Clinically, 11 (68%) pt had syncope or presyncope, 3 (18%) had dyspnea on exertion, and 2 (12.5%) were asymptomatic. Eight (50%) pt had bundle-branch block as follows: 4 (25%) pt had left bundle-branch block, and 4 (25%) had right bundle-branch block. Left anterosuperior divisional block was observed in 3 pt (19%), 2 of whom with associated right bundle-branch block. CONCLUSION: Intra-His bundle block was observed in 11% of the pt with second-degree atrioventricular block, syncope or presyncope, or both, it being the most frequent clinical presentation. Intra-His bundle block was more common in the elderly (> 60 years) and among females. The most frequent electrocardiographic presentations were second-degree Mobitz I or type 2:1 atrioventricular block.