Possibilities of Checking Water Content in Porous Geopolymer Materials Using Impedance Spectroscopy Methods

The porous geopolymer has been tested for its content of water using impedance methods. The pores of the material were filled with distilled water using a desiccator and a vacuum pump. An analysis of differential scanning calorimetry (DSC) was carried out in the next step to check the content of water, porosity and approximate value of specific heat of the geopolymer. Additionally, mercury porosimeter has been used for checking the porosity. The geopolymer material characterized in this way was subjected to impedance tests aimed at developing a quick method for assessing the water content in the material. Impedance measurements have been realized on an electrochemical workstation applying a 50 mV non-destructive amplitude of the potential and a frequency range of 1 Hz to 100 kHz. Change in the module of impedance and the phase shift angle were measured while the material was dried out. Significant differences were observed. The obtained graphs were simulated using a schematic model consisting of constant phase elements (CPEs) and a resistor (R). These values showed mechanisms of charge conduction. A simple method for assessing the water content of a porous geopolymer has been proposed in this paper. The real and imaginary impedance values were shown in Nyquist graphs. These graphs have characteristic maxima that move according to a linear equation with decreasing water content. Changes in Nyqiust charts are clearly visible even with small changes in the water content of the material and can be very useful for assessing it.

Murine typhus in South Texas children

BACKGROUND

Murine typhus is a zoonotic infection caused by Rickettsia typhi. This illness used to be endemic in the southeastern and gulf coast of the United States and is now only rarely reported in South Texas and Southern California. Murine typhus causes a febrile illness with headache and rash that has been well-described in adults.

OBJECTIVE

To define the epidemiologic and clinical characteristics, laboratory findings, hospital course and response to therapy of children discharged from our hospital with a diagnosis of murine typhus.

METHODS

Retrospective chart review of all children discharged from Driscoll Children's Hospital, Corpus Christi, TX, from January 1, 1990, to June 30, 1998, with a diagnosis of murine typhus. Patients. Thirty children (17 females) ages 2 to 17 years (mean, 10 +/- 4 years).

RESULTS

Eighty percent of the children were admitted between May and November, and 67% had a history of contact with or exposure to a potential animal reservoir. Children were admitted after a mean of 7 +/- 4 days. The most common clinical features were fever 100%, rash 80% and headache 77%. Laboratory abnormalities included elevated erythrocyte sedimentation rate (75%), elevated serum transaminases (67%), hyponatremia (66%) and increased immature leukocytes without leukocytosis (63%). Only one child had leukocytosis and 40% had leukopenia. Defervescence occurred a mean of 35 +/- 19 h after initiation of appropriate antibiotics. Hospitalization lasted for a mean of 7 +/- 3 days. There were no readmissions and no patients died as a result of the infection.

CONCLUSIONS

Despite being rarely reported in this country now, murine typhus continues to be an important cause of fever and hospitalization for children in South Texas. Children with murine typhus develop an illness similar to that reported in adults with fever, rash and headache. Children respond quickly to therapy with doxycycline or tetracycline and recover completely from their illness.