RESUMO
The topological Hall effect (THE) is the transport response of chiral spin textures and thus can serve as a powerful probe for detecting and understanding these unconventional magnetic orders. So far, the THE is only observed in either noncentrosymmetric systems where spin chirality is stabilized by Dzyaloshinskii-Moriya interactions, or triangular-lattice magnets with Ruderman-Kittel-Kasuya-Yosida-type interactions. Here, a pronounced THE is observed in a Fe-Co-Ni-Mn chemically complex alloy with a simple face-centered cubic (fcc) structure across a wide range of temperatures and magnetic fields. The alloy is shown to have a strong magnetic frustration owing to the random occupation of magnetic atoms on the close-packed fcc lattice and the direct Heisenberg exchange interaction among atoms, as evidenced by the appearance of a reentrant spin glass state in the low-temperature regime and the first principles calculations. Consequently, THE is attributed to the nonvanishing spin chirality created by strong spin frustration under the external magnetic field, which is distinct from the mechanism responsible for the skyrmion systems, as well as geometrically frustrated magnets.
RESUMO
OBJECTIVE: To study the effect of methylprednisolone (MP) on reperfusion injury in severe uncontrolled hemorrhagic shock and explore the possible mechanism involved. METHODS: Twelve dogs were randomly divided into two groups, control group (Group I, n=6) and MP group (Group II, n=6). The animals were bled continuously from a femoral artery catheter to produce uncontrolled hemorrhagic shock models. Resuscitation with lactated Ringer's (LR) solution was initiated when mean arterial pressure (MAP) decreased to 20 mm Hg, and MAP was maintained at 30-40 mm Hg. MP (4 mg/kg) was injected intravenously in Group II when resuscitation began. While in Group I, normal saline (NS) was injected instead. The levels of superoxide dismutase (SOD) and malondialdehyde (MDA) were measured before exsanguination (T(1)), when MAP decreased to 20 mm Hg (T(2)), 60 min (T(3)) and 120 min (T(4)) after resuscitation. Heart rate, MAP and cardiac output (CO) levels were recorded concomitantly. RESULTS: Infusion volume and hemorrhage volume shed from the superior mesenteric artery in Group I were higher than those in Group II (P<0.01 and P<0.05). After reperfusion, blood SOD levels decreased progressively and MDA levels increased rapidly in Group I. In Group II, blood SOD levels at T(3) and T(4) decreased as compared with that at T(1) but a stepwise increase was present. At T(4), blood SOD level was significantly higher in Group II than in Group I (Plt;0.01). At T(3) and T(4), MDA levels were markedly lower in Group II than in Group I. During reperfusion, MAP was more steady in Group II than in Group I and survival rate after 120 min (at T(4)) was higher in Group II than in Group I (P<0.05). CONCLUSIONS: MP has a protective effect on severe uncontrolled hemorrhagic shock and subsequent reperfusion injury. The mechanism mainly involves the anti-lipid peroxidation activity of MP.