Investigating the magnetic and magnetocaloric behaviors of LiSm(PO3)4

We report a detailed study on the magnetic behaviors and magnetocaloric (MC) effect of a single crystal of lithium samarium tetraphosphate, LiSm(PO₃)₄. The analyses of temperature-dependent magnetization data have revealed magnetic ordering established with decreasing temperature below T _p, where T _p is the minimum of a dM/dT vs. T curve and varies as a linear function of the applied field H. The Curie temperature has been extrapolated from T _p(H) data, as H → 0, to be about 0.51 K. The establishment of magnetic-ordering causes a substantial change in the heat capacity C _p. Above T _p, the crystal exhibits paramagnetic behavior. Using the Curie-Weiss (CW) law and Arrott plots, we have found the crystal to have a CW temperature θ _CW ≈ -36 K, and short-range magnetic order associated with a coexistence of antiferromagnetic and ferromagnetic interactions ascribed to the couplings of magnetic dipoles and octupoles at the Γ₇ and Γ₈ states. An assessment of the MC effect has shown increases in value of the absolute magnetic-entropy change (|ΔS _m|) and adiabatic-temperature change (ΔT _ad) when lowering the temperature to 2 K, and increasing the magnetic-field H magnitude. Around 2 K, the maximum value of |ΔS _m| is about 3.6 J kg^-1 K^-1 for the field H = 50 kOe, and ΔT _ad is about 5.8 K for H = 20 kOe, with the relative cooling power (RCP) of ∼82.5 J kg^-1. In spite of a low MC effect in comparison to Li(Gd,Tb,Ho)(PO₃)₄, the absence of magnetic hysteresis reflects that LiSm(PO₃)₄ is also a candidate for low-temperature MC applications below 25 K.

A comparison of epidural versus general anesthesia for outpatient endoscopic preperitoneal herniorrhaphy

OBJECTIVES

To study the efficacy of epidural versus general anesthesia on length of stay, patient recovery and anesthetic-related complications in patients undergoing endoscopic preperitoneal herniorrhaphy.

METHODS

One hundred sixty-seven consecutive patients undergoing endoscopic preperitoneal herniorrhaphy from July, 1994, to August, 1995, were retrospectively studied. A total of 243 herniorrhaphies were performed. Four patients required conversion of epidural anesthesia to general anesthesia because of inadequate sensory blockade (67/71; 94% success rate). One-hundred-forty-eight patients were available for review. Sixty-seven patients underwent successful epidural anesthesia during the case, while 81 patients were managed with general anesthesia.

RESULTS

Thirty patients (37%) receiving general anesthesia required interventions for nausea compared to only six patients (9.0%) in the epidural anesthesia group (p < 0.001). Thirty patients (37%) in the general anesthesia group required intervention because of complaints of pain, compared to 13 (19.4%) in the epidural group (p < 0.05). There were no differences between the two groups for length of stay in OR, PACU, or total hospital times.

CONCLUSIONS

The use of epidural anesthesia during the performance of endoscopic preperitoneal herniorrhaphy was associated with a decrease in the incidence of postoperative pain and nausea. The technique was successful in 94% of the cases in which it was used. Epidural anesthesia is recommended as an effective alternative to general anesthesia for the performance of outpatient endoscopic preperitoneal herniorrhaphy.