A comparative neutron and gamma-ray radiation shielding investigation of molybdenum and boron filled polymer composites

This work presents a detailed radiation shielding study for polymer composites filled with Boron and Molybdenum additives. The chosen novel polymer composites were produced at different percentages of the additive materials to provide a proper evaluation of their neutron and gamma-ray attenuation abilities. The effect of additive particle size on the shielding characteristics was further investigated. On the gamma-ray side, simulation, theoretical and experimental evaluations were performed in a wide range of photon energies varying from 59.5 keV to 1332.5 keV with help of MC simulations (GEANT4 and FLUKA), WinXCOM code, a High Purity Germanium Detector, respectively. A remarkable consistency was reported between them. On the neutron shielding side, the prepared samples produced with nano and micron particle size additives were additionally examined by providing fast neutron removal cross-section (Σ_R) and the simulated neutron transmissions through the prepared samples. The samples filled with nano sized particles show better shielding capability than the one filled with micron sized particles. In other words, a new polymer shielding material that does not contain toxic content is introduced: the sample codded N-B0Mo50 exhibits superior radiation attenuation.

A detailed investigation of gamma and neutron shielding capabilities of ternary composites doped with polyacrylonitrile and gadolinium (III) sulfate

The shielding efficiencies of gamma and neutron radiations for ternary composites containing polyester resin, polyacrylonitrile and gadolinium (III) sulfate at different ratios were investigated in the present study. In order to investigate the gamma radiation shielding capacity of the produced ternary composites, linear and mass attenuation coefficients, half value layer, effective atomic number and radiation protection efficiency parameters were determined experimentally, theoretically and using the GEANT4 simulation code. The gamma shielding capabilities of the composites were studied in the photon energy range of 59.5-1332.5 keV. In order to investigate the neutron shielding abilities of composites, inelastic, elastic, capture and transport numbers, total macroscopic cross section and mean free path parameters were determined with the help of GEANT4 simulation code. In addition, the number of transmitted neutrons at different sample thicknesses and neutron energies were also determined. It was observed that gamma radiation shielding properties were improved due to the increasing amount of gadolinium (III) sulfate and neutron shielding properties were improved due to the increasing amount of polyacrylonitrile. While the composite coded P0Gd50 exhibits a better gamma radiation shielding ability than the others, the neutron shielding of the sample coded P50Gd0 is also more favorable than the others.

Optimal patient position for percutaneous nephrolithotomy in horseshoe kidneys: Traditional prone or supine?

OBJECTIVE

Although it was stated that supine percutaneous nephrolithotomy (PCNL) was associated with relatively shorter surgical times and comparable success and complication rates, there is no consensus in the current literature concerning the safety and efficacy of supine PCNL in patients with horseshoe kidneys. We aimed to compare supine and prone PCNL regarding safety and efficacy in patients with horseshoe kidneys.

METHODS

Data of the patients with horseshoe kidneys who underwent PCNL for renal stones larger than 2 cm between January 2010 and May 2021 were retrospectively reviewed. The study patients were categorized as Group 1 (i.e., supine PCNL-SPCNL) and Group 2 (i.e., prone PCNL-PPCNL). Both groups were compared regarding demographic, clinical, and surgical data.

RESULTS

Sixty-five patients were included. Among these patients, 31 (47.7%) were in Group 1, while 34 (52.3%) were in Group 2. Both groups were statistically similar in terms of demographic data, stone characteristics, perioperative parameters, and complication rates (p > 0.05). There was no statistical difference in terms of additional treatment rates, stone-free rates in the postoperative second-day and third-month evaluations (p > 0.05). Mean surgical time was significantly longer in Group 2 (113 ± 17.1 min) than in Group 1 (90.6 ± 11.3 min) (p = 0.000).

CONCLUSION

Although it is traditionally performed in the prone position, the supine approach is as safe and effective as the prone approach. In addition, the supine approach is associated with significantly shorter surgical times.

Potential application of cryogenic freezer on turbot sperm cryopreservation

BACKGROUND

Cryopreservation is a common practice to preserve fish sperm for prolonged periods.

OBJECTIVE

To examine the effect of different freezing protocols on sperm characteristics, fertilization, and hatching rate of turbot.

MATERIALS AND METHODS

Milt was obtained from ten 8-year-old turbot (54.3 ± 1.7 cm in length and 3,106 ±283 g in weight) at the peak of spawning season. Six batches of milts with >90% motility was pooled and diluted to 1:3 by adding dimethyl sulfoxide (DMSO, 10%) as cryoprotectant. Then straws filled with semen were subjected to three freezing protocols (cooling rates). Sperm characteristics were assessed using sperm class analyzer before and after cryopreservation. Cryopreserved and fresh sperm were used for artificial fertilization to assess fertilization and hatching rates.

RESULTS

Cryopreservation protocol has significantly deleterious effects on total motility, progressive motility, curvilinear velocity, straight line velocity, average path velocity, linearity index, straightness index, oscillation index, and amplitude of lateral head displacement of sperm. However, the beat frequency of cryopreserved sperm was found to be similar to control sperm. The fertilization rate of sperm subjected to three freezing protocols were similar, varying between 65.3 % and 75.6 %, and the hatching rates varied from 51.2 % to 70.7 %.

CONCLUSION

The results show the potential application of cryopreservation in fish hatcheries. doi.org/10.54680/fr22410110312.

Dynamic thiol-disulfide homeostasis is disturbed in hepatitis B virus-related chronic hepatitis and liver cirrhosis

Background/aim: Thiol-disulfide homeostasis is an important antioxidant defense mechanism. This study was conducted to investigate dynamic thiol-disulfide homeostasis in patients with hepatitis B virus-related chronic hepatitis and liver cirrhosis. Materials and methods: Seventy-one treatment-naive patients with chronic hepatitis B (CHB), 50 patients with hepatitis B virusassociated liver cirrhosis, and 45 healthy controls were included in the study. Serum total and native thiol concentrations and serum disulfide concentrations were measured using an automated method. Results: Mean serum total thiol concentrations in the control, CHB, and cirrhosis groups were 481.64 ± 37.87 µmol/L, 438.50 ± 71.35 µmol/L, and 358.07 ± 80.47 µmol/L, respectively (P < 0.001), and mean serum native thiol concentrations in the control, CHB, and cirrhosis groups were 452.92 ± 36.43 µmol/L, 400.16 ± 65.92 µmol/L, and 328.15 ± 74.91 µmol/L, respectively (P < 0.001). Mean serum disulfide concentrations in the control, CHB, and cirrhosis groups were 14.38 ± 3.38 µmol/L, 19.19 ± 6.16 µmol/L, and 14.98 ± 5.53 µmol/L, respectively (P < 0.001). There was a progressive decrease in both mean serum native and total thiol concentrations parallel to the liver fibrosis stage. Conclusion: : Thiol-disulfide homeostasis is disturbed in patients with hepatitis B virus-related chronic hepatitis and liver cirrhosis.

Is there any potential or additive effect of anemia on hepatorenal syndrome?

BACKGROUND/AIMS

Hepatorenal syndrome (HRS) is a severe complication of advanced cirrhosis and is characterized by renal dysfunction and poor survival rates. Although anemia is a non-rare condition in advanced liver cirrhosis, there is no publication regarding the potential or additive effects of anemia on HRS and renal dysfunction in patients with cirrhosis. We investigated whether severe anemia is a precipitant factor for HRS.

MATERIALS AND METHODS

In this prospective study, consecutive patients with cirrhosis with and without renal dysfunction were enrolled. A total of 29 patients with cirrhosis with HRS meeting the HRS diagnostic criteria (9 patients with type 1 HRS and 20 with type 2 HRS) and 37 patients with cirrhosis without HRS were included. The demographic features, laboratory data (particularly anemic parameters), and clinical scores of patients with and without HRS were evaluated.

RESULTS

Grades of ascites, Child-Turcotte-Pugh (CTP) scores, and Model of End Stage Liver Disease (MELD) scores were significantly higher in contrast to hemoglobin levels; hematocrit concentrations were significantly lower in patients with type 1 and 2 HRS than in those with non-HRS stable cirrhosis. There was a negative correlation between the hemoglobin-hematocrit and serum creatinine levels. In the logistic regression analysis, the hemoglobin levels and CTP and MELD scores were statistically significant for an onset of HRS.

CONCLUSION

Anemia may contribute to HRS and deteriorated renal function in patients with HRS because anemic hypoxia can lead to microcirculatory renal ischemia in the kidneys and anemia can also activate sympathetic activity and hyperdynamic circulation in the pathogenesis of HRS.

Serum ischemic modified albumin (IMA) concentration and IMA/albumin ratio in patients with hepatitis B-related chronic liver diseases

BACKGROUND/AIM

Albumin is the most important protein synthesized by the liver. Posttranscriptional changes occur in the molecular structure of albumin due to various factors and isoforms arise. Ischemic modified albumin (IMA) is one such isoform. This study was conducted to evaluate serum IMA concentrations in patients with hepatitis B virus (HBV)-related chronic liver diseases.

MATERIALS AND METHODS

This study included 74 treatment-naive chronic hepatitis B patients, 25 patients with HBV-related cirrhosis, and 49 healthy controls. Serum IMA concentration was measured spectrophotometrically using the albumin cobalt binding test.

RESULTS

The mean IMA concentrations in the chronic hepatitis B group and healthy controls were 0.33 ± 0.11 ABSU and 0.27 ± 0.70 ABSU, respectively, and the difference was statistically significant (P < 0.001). Mean IMA/albumin ratios (IMAR) in the chronic hepatitis B and control groups were 0.08 ± 0.04 and 0.06 ± 0.17, respectively, and the difference was also statistically significant (P < 0.001). Higher serum IMA concentrations and IMAR were detected in patients with advanced fibrosis.

CONCLUSION

Serum IMA concentration and IMAR are increased in patients with HBV-related chronic liver diseases and IMA and IMAR are associated with the degree of liver fibrosis. IMA and IMAR may have potential use as noninvasive markers of fibrosis in chronic hepatitis B patients.

Hormonal synchronization of lipopolysaccharide-induced hypothermic response in rats

BACKGROUND

Recent experimental evidence suggests that lipopolysaccharide (LPS)-induced hypothermia is an adaptive thermoregulatory strategy against immunological challenge in rats. We hypothesized that the hormones which are predominantly responsible for energy homeostasis may have efferent signaling roles for development of the hypothermia.

AIM

The aim of the study was to evaluate the changes of hypothalamic-pituitary-thyroid (HPT) and hypothalamic- pituitary-adrenal (HPA) axis hormones, leptin and erythropoietin at various phases of LPS-induced hypothermia such as the initial phase, nadir and the end of the response in blood sampled rats.

MATERIAL AND METHODS

Body temperature of adult male albino Wistar rats was recorded by biotelemetry. E. coli O111:B4 LPS (250 μg/kg, ip) was injected alone or with SC-560, a cyclooxygenase-1 selective inhibitor (1 mg/kg, sc).

RESULTS

Serum FT4 levels elevated at the initial phase, but FT3 levels decreased at nadir and remained low at the end of the response. Meanwhile, no change was observed in TSH levels. Serum adrenocorticotropic hormone (ACTH) levels reduced at the initial phase and serum corticosterone levels decreased at nadir without any change in serum corticotropin-releasing hormone (CRH) levels throughout the hypothermia. Serum leptin levels increased only at the end of the response. No change was observed in the levels of serum erythropoietin. SC-560 treatment abolished both LPS-induced hypothermia and respective hormonal changes.

CONCLUSION

Data suggest that HPT axis hormones may contribute to development of LPS-induced hypothermia in rats. Data also support the view that leptin may have a role for the recovery of hypothermic response.

Plasma ω-3 fatty acid levels negatively and ω-6 fatty acid levels positively associated with other cardiovascular risk factors including homocysteine in severe obese subjects

Obesity and homocysteine (tHcy) are important risk factors for cardiovascular diseases (CVD). Plasma omega-3 fatty acids (ω-3 FAs) and omega-6 fatty acids (ω-6 FAs) are essential fatty acids with diverse biological effects in human health and disease. We have investigated the relation of plasma ω-3 FAs and ω-6 FAs levels with other cardiovascular risk factors including tHcy in severe obese subjects. This study was performed on 96 severe obese and 65 normal weight subjects. Plasma fatty acid composition was measured by GC/MS and serum tHcy level was measured by HPLC methods. There were no differences between groups in terms of concentrations of serum tHcy, plasma ω-3 FAs, ω-6 FAs and ω-3/ω-6 ratio, whereas serum vitamin B-12 (p<0.01) and folic acid (p<0.05) levels were lower than those of the normal weight subjects. Homocysteine positively correlated with ω-6 FAs and negatively correlated with ω-3 FAs in severe obese and normal weight subjects. Serum vitamin B-12 positively correlated with ω-3 FAs (p<0.01) and ω-3/ω-6 ratio (p<0.01) and negatively correlated with ω-6 FAs (p<0.05) in severe obese subjects. Serum folic acid positively correlated with ω-3 FAs (p<0.01) in severe obese subjects. Our results suggest an association between the plasma ω-3 FAs and ω-6 FAs and serum tHcy concentrations in severe obese and normal weight subjects. Low levels vitamin B-12 and folic acid may have been responsible for the elevated tHcy levels in severe obese subjects, increasing the risk for future development of cardiovascular diseases.

Obesity is an independent determinant of ischemia-modified albumin

OBJECTIVE

We have measured ischemia-modified albumin (IMA), total antioxidant status (TAS), total oxidant status (TOS) and high-sensitivity C-reactive protein (hsCRP) levels in obese and normal-weight subjects to investigate if IMA can be used as a biomarker of oxidative stress and inflammation and if IMA was an independent determinant of obesity or not.

METHODS

The study was performed on 92 obese subjects (20 male, 72 female) aged 38 ± 11 years and 78 normal-weight controls (19 male, 59 female) aged 37 ± 11 years. Serum lipids, IMA, TAS, TOS, and hsCRP levels of the subjects were measured.

RESULTS

IMA (p < 0.05), TOS (p < 0.001), and hsCRP (p < 0.001) levels of the obese subjects were significantly higher, whereas TAS levels were significantly lower (p < 0.05) than those of the controls after adjustment for age and gender. In the linear regression analysis, waist circumference (r² = 0.139, p < 0.01), BMI (r² = 0.136, p < 0.01) and insulin (r² = 0.120, p < 0.05) were shown to be significant independent determinants of IMA levels.

CONCLUSIONS

We have found that oxidative stress and inflammation were increased and antioxidative defense was decreased, which resulted in increased levels of IMA, a biomarker of ischemia, in obese subjects. Also, obesity and insulin were found to be independent determinants of IMA. Thus, obese subjects are under high risk of ischemia, and IMA may be used as a biomarker of oxidative stress and ischemia. Further larger investigations are needed to confirm this opinion.

Encapsulating fly ash and acidic process waste water in brick structure

Fly ash contains metals such as cadmium, iron, lead, aluminum and zinc in its structure in appreciable amounts. These metals can leach out into surface and ground waters if fly ash is not properly disposed of. A similar problem also exists for acidic process waste waters discharged by numerous industries. The purpose of this study was to utilize such wastes as additives in the production of construction quality bricks for the purpose of waste elimination. The bricks produced were subjected to flexural strength and water retention capacity tests along with heavy metal leaching experiments in order to determine the applicability of the procedure and the best possible recipes. This paper summarizes the results obtained in these tests along with the possible mechanisms involved in stabilizing the two wastes in the brick structure.

Analytical solution of Poisson-Boltzmann equation for interacting plates of arbitrary potentials and same sign

Efficient calculation of electrostatic interactions in colloidal systems is becoming more important with the advent of such probing techniques as atomic force microscopy. Such practice requires solving the nonlinear Poisson-Boltzmann equation (PBE). Unfortunately, explicit analytical solutions are available only for the weakly charged surfaces. Analysis of arbitrarily charged surfaces is possible only through cumbersome numerical computations. A compact analytical solution of the one-dimensional PBE is presented for two plates interacting in symmetrical electrolytes. The plates can have arbitrary surface potentials at infinite separation as long they have the same sign. Such a condition covers a majority of the colloidal systems encountered. The solution leads to a simple relationship which permits determination of surface potentials, surface charge densities, and electrostatic pressures as a function of plate separation H for different charging scenarios. An analytical expression is also presented for the potential profile between the plates for a given separation. Comparison of these potential profiles with those obtained by numerical analysis shows the validity of the proposed solution.

The WHO global alliance against chronic respiratory diseases in Turkey (GARD Turkey)

In order to prevent and control non-communicable diseases (NCDs), the 61st World Health Assembly has endorsed an NCD action plan (WHA resolution 61.14). A package for essential NCDs including chronic respiratory diseases (CRDs) has also been developed. The Global Alliance against Chronic Respiratory Diseases (GARD) is a new but rapidly developing voluntary alliance that is assisting World Health Organization (WHO) in the task of addressing NCDs at country level. The GARD approach was initiated in 2006. GARD Turkey is the first comprehensive programme developed by a government with all stakeholders of the country. This paper provides a summary of indicators of the prevalence and severity of chronic respiratory diseases in Turkey and the formation of GARD Turkey.

Thalassaemia screening in a non-prevalent region of a prevalent country (Turkey): is it necessary?

OBJECTIVES

Haemoglobinopathies are the most widespread inherited disorders in the world, and are also common in Turkey. Haemoglobinopathies are preventable with control programmes. Therefore, the Ministry of Health initiated a control and prevention programme in 33 provinces in Turkey. The aim of this study was to determine the frequency of haemoglobinopathies in Erzurum as part of the programme mentioned above, and to discuss the need for premarital screening in a non-prevalent region (Erzurum) of a prevalent country (Turkey) as part of a national control programme.

STUDY DESIGN

Epidemiological and descriptive survey.

METHODS

This study was conducted between May 2005 and February 2006 in Erzurum. Subjects were couples who attended for premarital screening. All blood samples were measured by high-performance liquid chromatography (HPLC) to determine haemoglobinopathies.

RESULTS

In total, 1610 individuals were screened. The frequency of beta-thalassaemia trait was 0.68%. Haemoglobin D was the most common (0.12%) abnormal haemoglobin. Haemoglobins S, C and E were not detected. The frequency of beta-thalassaemia trait and other haemoglobinopathies in Erzurum was quite low compared with other provinces in Turkey.

CONCLUSIONS

Premarital haemoglobinopathy screening should not be mandatory in a non-prevalent region of a prevalent country as part of a national control programme. If screening is mandatory, it should be performed by total blood count or enzyme-linked immunosorbent assay, which are simple, rapid and less expensive than HPLC.

Heavy metal removal from waste waters by ion flotation

Flotation studies were carried out to investigate the removal of heavy metals such as copper (II), zinc (II), chromium (III) and silver (I) from waste waters. Various parameters such as pH, collector and frother concentrations and airflow rate were tested to determine the optimum flotation conditions. Sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide were used as collectors. Ethanol and methyl isobutyl carbinol (MIBC) were used as frothers. Metal removal reached about 74% under optimum conditions at low pH. At basic pH it became as high as 90%, probably due to the contribution from the flotation of metal precipitates.

Effect of various treatment and glazing (coating) techniques on the roughness and wettability of ceramic dental restorative surfaces

Surface treatment procedures such as grinding and polishing are needed to provide the ceramic dental restorative materials with proper fitting and occlusion. The treated surfaces are customarily glazed to improve the strength and smoothness. Though smoothness and wetting of the dental surfaces are important to minimize bacterial plaque retention, influence of the surface treatment and glazing procedures on the final surface roughness and its correlation to wettability are overlooked. In this work, effect of various treatment (diamond fraising, stoning, sanding and aluminum oxide and rubber polishing) and glazing (auto and overglazing) techniques on the final roughness and the resulting wettability of dental ceramic surfaces were investigated using scanning electron microscopy (SEM) observations and atomic force microscopy (AFM) scans, 75 scans per sample. The surfaces were characterized and assigned an average roughness measure, R(a). The wettability of the same surfaces was evaluated using micro-contact angle measurements (25 micro-bubbles placed on a grid on each surface) to correlate the final surface roughness and wettability. The results show that overglazing prevails over surface irregularities from different treatment procedures and provides homegeneously smooth surfaces with mean R(a)<10 nm. It also produces uniformly wetted surfaces with low contact angles around 20 degrees . The autoglazed surfaces are less smooth (mean R(a) around 50 nm) and displays sporadic topographic irregularities. They display larger and less uniform contact angles ranging between 35 degrees and 50 degrees . The results suggest that overglazing should be preferred after surface treatment to obtain a smooth and well-wetted dental ceramic surface.

Adult intussusception secondary to inflammatory fibroid polyp: demonstration by MRI

Adult intussusception secondary to inflammatory polyp occurs rarely. Imaging of intussusception on ultrasound, CT and MRI has been previously described. In this report we describe a case of an adult intussusception secondary to inflammatory fibroid polyp. Both the lead point (inflammatory fibroid polyp) and intussusception were depicted on multiplanar MR images. Findings on MRI were confirmed at surgery and histopathological examination.

Bioelectrical impedance analysis as a predictor of survival in patients with human immunodeficiency virus infection

In patients with AIDS, short-term survival has been related to body weight, body composition, and serum nutritional parameters, but their prognostic impact at earlier stages of the HIV infection is not known. With an individual follow-up period of 1,000 days, we investigated the prognostic relevance of electrical tissue conductivity [resistance R, reactance Xc, phase angle alpha, extracellular mass (ECM), body cell mass (BCM)] measured by bioelectrical impedance analysis, of the CD4+ cell count, and of serum parameters indicating malnutrition in 75 HIV-infected male patients at Walter Reed stages 3-5. After initial recording, 29 patients (38.7%) died from AIDS during this period. Among 12 parameters estimated with a semiparametric Cox regression model adjusted for therapy (pentamidine, azidothymidine), the phase angle alpha (parameter estimate: -1.043, 95% confidence interval of -0.61 to -1.47; p < or = 0.0001), the ECM/BCM ratio, Xc, BCM, serum cholesterol, number of CD4+ cells, and serum albumin had significant prognostic influence on survival, whereas age, body weight, body mass index, resistance, serum protein, and serum triglycerides did not. In a model with four covariates (CD4+ cells, phase angle, pentamidine, azidothymidine), the prognostic impact of the CD4+ cell count (parameter estimate: -0.549) was lower compared with the phase angle alpha (parameter estimate: -0.799; p < or = 0.0001) and did not gain statistical significance (p = 0.0626). The phase angle alpha was the best single predictive factor for survival among all 12 parameters (comparison of the respective Cox models with the likelihood ratio test).(ABSTRACT TRUNCATED AT 250 WORDS)

Early changes of body composition in human immunodeficiency virus-infected patients: tetrapolar body impedance analysis indicates significant malnutrition

Total body water, body fat, body cell mass (BCM), extracellular mass (ECM), and the ECM-BCM ratio by impedance analysis were determined in 193 human immunodeficiency virus (HIV)-infected patients and 340 control subjects. Walter Reed (WR) classification was WR 2 in 26, WR 3-5 in 85, and WR 6 in 82 patients. Whereas resistance was increased, reactance and the phase angle were significantly reduced in all patient groups. Neither body weight nor body mass index (BMI) was affected in WR 2 patients, but BCM was reduced (31.9 +/- 4.3 vs 35.8 +/- 7.3 kg, P < 0.007) and ECM (31.2 +/- 4.4 vs 28.8 +/- 3.8 kg) as well as ECM-BCM ratio increased (0.99 +/- 0.14 vs 0.83 +/- 0.16, P < 0.001). In contrast to WR classification, diarrhea did not correspond with malnutrition. A loss of BCM (malnutrition) occurred already in otherwise symptomless HIV-infected patients (WR 2). This effect can be measured by tetrapolar impedence analysis but not by body weight or BMI.

Sodium ipodate in the treatment of toxic diffuse goiter. Short-term and long-term effects on thyrotoxicosis

Iodinated radiocontrast medication has been successful in the treatment of thyrotoxicosis when used for short periods up to 21 days, but experience with long-term use is lacking. In the first part of this study, a group of seven patients each taking 1.5 g. sodium ipodate daily was observed for 21 days and compared to a similar group of seven thyrotoxic patients taking 400 mg. propylthiouracil (PTU) daily. Sodium ipodate brought about a more significant decrease in serum total T3 and T4 levels, and more prominent increase in reverse T3 levels in the first ten days of the treatment. In the second part, a group of seven patients with thyrotoxicosis were given sodium ipodate, 1.5 g, daily for 20 days and 0.75 g. thereafter and were compared to a similar group of seven patients who took PTU, 300 mg. daily for the first 20 days and 150 mg. daily afterwards. Serum thyroid hormone levels decreased in both groups at the end of the first month of treatment, but rose again, along with worsening of symptoms, in five patients on ipodate treatment. Therefore, sodium ipodate, an iodinated radiocontrast agent is unable to control thyrotoxicosis for longer than a month.