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1

Electronic Resource

Dielectric properties of BaTiO3/SrTiO3 multilayered thin films prepared by pulsed laser deposition (1998)

Qu, B. D. ; Evstigneev, M. ; Johnson, D. J. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 72 (1998), S. 1394-1396

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: BaTiO3/SrTiO3 multilayered thin films were deposited on Si and Pt/Si substrates. X-ray diffraction clearly shows the formation of the superstructures. Phase transition properties were studied via dielectric measurements. Glassy behavior, characterized by a strong frequency dispersion of dielectric properties, was found in samples with a total thickness of 400 nm, while in samples with a total thickness of 800 nm, normal ferroelectric phase transitions with two dielectric peaks were observed. A preliminary interpretation assumes that size effects which frustrate long range ferroelectric ordering may lead to the relaxational behavior in BaTiO3/SrTiO3 superstructures. © 1998 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.121066

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2

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Elemental composition of a tusk of a dugong, Dugong dugon, from Exmouth, Western Australia (1997)

Edmonds, J. S. ; Shibata, Y. ; Prince, R. I. T. ; [et al.]

Springer

Marine biology 129 (1997), S. 203-214

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ISSN: 1432-1793

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Element analysis of the annual increments in a longitudinal section from the tusk of a female dugong Dugong dugon (Müller) from Exmouth, Western Australia, was carried out by X-ray fluorescence-imaging, inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Nine elements (Ba, Ca, Fe, Li, Mg, Na, P, Sr and Zn) were present in concentrations amenable to determination by these techniques. Most elements revealed both long-term trends and shorter, year-to-year, variations. For example, sodium concentrations increased from 0.55 to 0.72% with the age of the dugong. Strontium concentrations (mean 0.17%) were closely correlated (r = 0.86) with those of barium (mean 4.5 mg kg−1). Zinc concentrations increased from ∼70 to 170 mg kg−1 with dugong age, but also showed shorter-term fluctuations of ∼30 mg kg−1 that were correlated (r = 0.41) with mean annual Fremantle sea level (a measure of the Southern Oscillation Index and strength of the Leeuwin Current). The concentrations of the elements and correlations with year and between pairs of elements are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002270050161

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3

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Practice Guidelines for the Treatment of Osteoporosis (1996)

Prince, R. L.

Springer

Calcified tissue international 59 (1996), S. S020

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ISSN: 1432-0827

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine , Physics

Notes: Abstract. History will probably describe this as a significant era for osteoporosis management, which has recently shifted from the laboratory and research clinic into mainstream clinical practice. It is timely, therefore, to provide practice guidelines for clinical use in this area; they must be developed carefully, however, so as to ensure that they are generated from reliable data. Furthermore, in current circumstances, management not only must be effective but also must aim for cost minimization; this is a difficult area in which little information is available. Also, in light of increased knowledge about skeletal medicine, complex cases should be considered for referral to an expert. The diagnosis of osteoporosis centers on two main steps: the identification of patients at risk and the estimation of bone density at two skeletal sites to help in ascertaining future fracture risk. At present, the main question in this approach centers on identifying the risk level threshold at which bone density should be evaluated. Although it is generally agreed that anyone with an atraumatic osteoporotic fracture will benefit from bone density estimation, the exact risk level for other, less easily defined indicators (e.g., cigarette smoking) is unclear. Once the diagnosis of osteoporosis is made, the cause must be elucidated by appropriate biochemical and imaging techniques. Appropriate therapy varies with the cause and level of risk. Although many treatments are currently available, including pharmacologic intervention, dietary changes, and exercise, they must be selected and adapted according to the needs of the individual patient, a process requiring both skill and patience.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002239900171

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4

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The Effect of Estrogen Deficiency on Calcium Balance in Mature Rats (1999)

Draper, C. R. ; Dick, I. M. ; Prince, R. L.

Springer

Calcified tissue international 64 (1999), S. 325-328

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ISSN: 1432-0827

Keywords: Keywords: Calcium balance — Estrogen deficiency — Rats — Intestine.

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine , Physics

Notes: Abstract. The role of estrogen in the regulation of calcium balance is still poorly understood. A calcium balance study was performed to examine the effects of estrogen status in relation to fecal calcium loss as a component of bone loss after oophorectomy (OOX) in the mature rat. The components of the classic calcium balance were compared with calcium balance estimates obtained from whole body bone density. Six month or older Sprague Dawley rats were allocated to either a sham-operated or OOX group and fed a 0.1% calcium diet. The bone mineral density (BMD) and bone mineral content (BMC) were measured at baseline, 6 weeks, and 9 weeks. A calcium balance was done for 6 days before and 6 weeks post OOX. The fall in BMD from baseline to 9 weeks in the OOX group was significantly greater than in the sham-operated group. The calcium balance was more negative at baseline than at 6 weeks in both groups of animals because they had not adapted to the low calcium diet. However, the increase in calcium balance was significantly less in the OOX animals than in the sham-operated animals. The greater the rise in calcium balance from the baseline to the 6 weeks balance the less the fall in the calcium content of the whole body (Spearman correlation: r = 0.604 P = 0.008). The fall in fecal calcium, but not urine calcium or calcium consumed, was negatively correlated with the change in whole body BMC (Spearman correlation: fecal calcium r =−0.763 P = 0.001). Thus, the primary effect of estrogen deficiency on calcium balance in the mature rat appears to be calcium flux in the bowel, rather than renal calcium handling.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002239900627

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5

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17β-estradiol suppresses gene expression of tartrate-resistant acid phosphatase and carbonic anhydrase II in ovariectomized rats (1995)

Zheng, M. H. ; Lau, T. -T. A. ; Prince, R. ; [et al.]

Springer

Calcified tissue international 56 (1995), S. 166-169

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ISSN: 1432-0827

Keywords: Tartrate-resistant acid phosphatase ; Carbonic anhydrase II ; Gene expression ; Estrogen ; Ovariectomy

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine , Physics

Notes: Abstract Tartrate-resistant acid phosphatase (TRACP) and carbonic anhydrase II (CA II) are key enzymes responsible for osteoclastic bone resorption. In this study, we proposed that estrogen loss in postmenopausal osteoporosis may enhance gene expression of TRACP and CA II, and subsequently increase osteoclastic bone resorption. We have, therefore, used the ovariectomized rat model of postmenopausal bone loss to investigate changes at the gene transcripional level in osteoclastic bone-resorbing enzymes in ovariectomized (OVX) rats, sham ovariectomized (S-OVX) rats, and estrogen-treated ovariectomized (E-OVX) rats. We have demonstrated for the first time that ovariectomy in rats enhances gene expression of TRACP and CA II. The mRNA levels in OVX were approximately three- and four-fold higher, respectively, than those in S-OVX. Enhancement was observed 1 week after ovariectomy and transcripts remain high during the experimental period of 8 weeks. Administration of 17β-estradiol to OVX (E-OVX) reduced gene expression of these osteoclastic bone-resorbing enzymes 18 hours after injection. It appeared that the suppression of the osteoclastic bone-resorbing enzymes by 17β-estradiol was most effective during the first 1–2 weeks but the degree of suppression was reduced at 8 weeks after ovariectomy. In conclusion, our results suggest that estrogen prevents bone loss by reducing the mRNA levels of osteoclastic bone-resorbing enzymes in bone tissue.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00296350

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6

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The Effect of Estrogen Deficiency on Bone Mineral Density, Renal Calcium and Phosphorus Handling and Calcitropic Hormones in the Rat (1996)

Dick, I. M. ; St. John, A. ; Heal, S. ; [et al.]

Springer

Calcified tissue international 59 (1996), S. 174-178

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ISSN: 1432-0827

Keywords: Key words: Oophorectomized rat — Calcitropic hormones — Calcium — Phosphorus — Kidney — Bone mineral density.

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine , Physics

Notes: Abstract. The oophorectomized (OOX) rat has been proposed as a good model of postmenopausal osteroporosis in women. The aim of this study was to compare the effect of OOX in 6-month-old rats to the effects of menopause in women with respect to bone mass, the renal handling of calcium and phosphorus, and calcitropic hormones. To more closely replicate the human situation the rats were pair fed a 0.1% calcium diet. Thirty four, 6-month-old rats were randomized to sham operation or OOX. Whole body and regional bone density was performed at baseline and 6 weeks postoperation. Blood and 24-hour urine samples were obtained at baseline, 1, 3, and 6 weeks and assayed for various biochemical variables, parathyroid hormone (PTH), and calcitriol. The OOX rats lost significantly more bone than the sham-operated rats (change in global bone mineral density, sham −1.7 ± 2.0%, OOX −3.9 ± 2.6%, P 〈 0.001). In the OOX animals, an increase in the 24-hour urine calcium was observed at 1 and 3 weeks, which had returned to sham-operated levels by 6 weeks. In the whole group, the increase in urine calcium at 1 week was negatively correlated with the change in bone mass at 6 weeks (r =−0.39, P= 0.029). OOX resulted in an increased filtered load of calcium and phosphorus. There was an increase in the maximal renal tubular reabsorption of phosphorus (TmP-GFR) but no clear change in renal calcium handling. Neither calcitriol nor parathyroid hormone showed a significant change as a result of OOX. As in postmenopausal women, following oophorectomy in the rat, there was significant generalized bone loss and a negative calcium balance. This was associated with an initial rise in urine calcium due to a rise in the filtered calcium load; plasma phosphorus and TmP-GFR also rose. The rat model may differ from postmenopausal bone loss in that the initial rise in urine calcium was not present at later time points as occurs in natural menopause in women. Calcitropic hormone levels did not change. This study has shown that the 6-month-old OOX rat fed a 0.1% calcium diet has many similarities of calcium and phosphorus homeostasis to that seen at menopause in women.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002239900105

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