Designing a tunable acoustic resonator based on defect modes, stimulated by selectively biased PZT rods in a 2D phononic crystal

Reconfigurable phononic crystals (PnCs) and related devices are highly attractive because of their flexibility for different applications. We present the design procedure for a tunable acoustic resonator based on a 2D PnC, consisting of a periodic array of piezoelectric rods of radii 175 μm as inclusions arranged in air background. A single point defect devised by a rod of radius 161 μm, replacing one of the inclusions, plays the role of the acoustic resonator, leading to a defect frequency in the phononic band gap (f_d ≈ 432 kHz). Applying a ∼1% strain to the defect rod, via an external voltage, tunes the defect resonant frequency within the phononic band gap. It is shown that the maximum tunability and the frequency shift depends on the defect size, and is achieved about Δf_d = 440 Hz for the defect with the expense of descending quality factor. Considering the pattern of the localized pressure field, we introduce a multi-defect structure with five symmetric defect rods, corresponding to the maxima of field distribution. It is shown that maximum frequency shift of the dominant defect frequency is achieved about Δf_d = 1.14 kHz for defect radius of 161 μm, when all five defect rods are strained. The proposed tunable filter based on multi-defect structure results in an enhancement of about 2.6 times in the maximum frequency shift, in comparison with the single defect structure, and introduces a promising approach for realizing tunable acoustic devices.

Selective and metal-free epoxidation of terminal alkenes by heterogeneous polydioxirane in mild conditions

Polydioxirane (PDOX) was prepared by the treatment of polysalicylaldehyde with Oxone and was found as a selective, highly efficient and heterogeneous reagent for epoxidation of alkenes which can be successfully isolated. This work also introduced a simpler, safer and milder way for epoxidation of alkenes with dioxirane groups than before. PDOX can be simply recovered from the reaction mixture by plain filtration and reused for eight runs without significant reactivity loss.

Co-infection of Malaria and Crimean-Congo Hemorrhagic Fever

Southeast of Iran is an endemic area for Malaria and Crimean-Congo hemorrhagic fever (CCHF). In 1999, we faced with an outbreak of CCHF in Sistan and Baluchistan Province, in the border of Pakistan and Afghanistan. The most cases of Malaria in Iran are also reported from this area. This article presents a 17-year- old woman who admitted to our hospital because of acute fever, headache, epistaxis, hemorrhagic lesions on the skin and vaginal bleeding. Finally, she was recognized as a case that was co -infected with CCHF and malaria.

Can Doppler ultrasonographic indices of the renal artery predict the presence of supernumerary renal arteries?

BACKGROUND

Variations of the renal arteries, including the presence of supernumerary renal arteries, are important to be identified prior to renal transplant. Angiography has been the gold standard test for the pretransplant evaluation of the renal vasculature. However, this modality is expensive and invasive. The aim of this study was to assess whether Doppler ultrasonographic (DU) indices of the renal artery could predict the presence of supernumerary renal arteries.

METHODS AND MATERIALS

Retrospectively, we analyzed multidetector computed tomography angiography (presence or absence of the supernumerary renal artery), DU (peak systolic velocity, resistive index, pulsatility index, end-diastolic velocity, and acceleration time) findings of 30 healthy potential renal transplant donors. Recipient operator characteristic (ROC) curves were used to examine the predictive values of the available DU indices for supernumerary renal arteries.

RESULTS

The mean age of donors was 28.4 +/- 4.1 years. Of 60 kidneys evaluated, a supernumerary renal artery was found in 10%. The ROC curve analysis revealed an area under the curve of noninformative (below 0.5) for all DU parameters, indicating that none of the studied parameters could predict the presence of a supernumerary renal artery.

CONCLUSIONS

Although the smaller diameter of the main renal artery has previously been found to predict the presence of supernumerary renal arteries, the present study revealed that DU indices of the renal artery may not indicate the presence of supernumerary renal arteries.

Screening for renal artery stenosis in patients with aorticoiliac occlusive disease

BACKGROUND

The prevalence of atherosclerotic renal artery disease has increased with improved life expectancy. Because renal artery stenosis is a potentially correctable cause of hypertension and ischemic nephropathy, early identification of this entity may lead to proper hypertension control and improved renal function and survival. The aim of this study was to determine the prevalence and patterns of subclinical renal artery stenosis in patients with aorticoiliac atherosclerosis.

PATIENTS AND METHODS

The abdominal angiographies of 44 patients with high-grade aorticoiliac occlusive disease (> 70% stenosis) were reviewed for evidence of renal artery stenosis. This was compared to a group of 20 patients with mild-to-moderate aorticoiliac disease (< 70% stenosis). These patients had no history of renal artery disease or renal failure.

RESULTS

In patients with high-grade aorticoiliac occlusive disease, renal artery stenosis was found in 25 patients (56.8%); 13 with unilateral (29.5%) and 12 (27.3%) with bilateral involvement. A hemodynamically significant stenosis (> 50%) was found in 11 patients (25%), one of whom had bilateral stenosis (2.3%). High-grade renal artery stenosis (> 70%) or complete arterial occlusion was noted on seven sides (7.9%). The most common sites of stenosis were the origin and first centimeter of the renal artery. In patients with mild-to-moderate aorticoiliac disease, renal artery stenosis was found in two patients (10%).

CONCLUSIONS

The present study revealed that subclinical renal artery disease may be present in more than half of the patients with high-grade aorticoiliac atherosclerosis highlighting the need for proper risk stratifications and screening programs. Based on our results, we suggest that examination of the renal arteries in these patients may be necessary in order to delay or prevent complications. Additionally, such information may have important therapeutic implications in planning reconstructive vascular surgeries or percutaneous angioplasties.