Parametrically excited nonlinear systems: a comparison of two methods

Subharmonic resonance of two-degree-of-freedom systems with cubic nonlinearities to multifrequency parametric excitations in the presence of three-to-one internal resonance is investigated. Two approximate methods (the multiple scales and the generalized synchronization) are used to construct a first-order nonlinear ordinary differential equations governing the modulation of the amplitudes and phases. Steady state solutions and their stability are computed for selected values of the system parameters. The results obtained by the two methods are in excellent agreement. Numerical solutions are carried out and graphical representations of the results are presented and discussed

Using time-independent analysis in optimizing inverter efficiency for grid-connected photovoltaic systems

A flexible and computationally effi cient analysis technique for designing and evaluating grid-connected photovoltaic (PV) systems is introduced, which establishes a direct relationship between the inputs to the system, temperature and irradiance, and system performance criteria. For a given year, temperature and irradiance data are rearranged to form a statistical distribution, eliminating thereby the direct time-dependence. The proposed technique decomposes the PV system into three separate layers: an ambient conditions, a PV output, and a dc-ac conversion layer. It reveals important trends, otherwise obscured in the time-dependent view of the data. The time-independent analysis technique is applied to the problem of optimizing inverter e ciency to improve the performance of residential PV systems. A parallel two-inverter con guration is proposed, where one inverter has a small rated power to handle the frequently occurring low-insolation conditions, while the other inverter is large enough to handle the high-insolation regime. The application of this new con guration leads to energy savings as well as e ciency and reliability improvements. A feasibility study taking into account the additional investments required to implement the suggested inverter con guration reveals that applying it under the current electricity prices does not make sense from the economic perspective. However, the two-inverter con guration can become an interesting option in the future as energy prices continue to rise and more nancial incentives for solar systems are introduced

Retrocaval ureter: a report on two neonates

Retrocaval ureter is a relatively rare anomaly that usually manifests in the third or the fourth decade of life. Its symptoms are because of ureteric obstruction, caused extrinsically by an abnormal inferior vena cava, intrinsically by ureteric hypoplasia, or both. Surgery is needed for symptomatic patients and involves transection and relocation of the ureter anterior to the inferior vena cava. We report here two neonates as might be very early diagnosed who needed surgery to correct a retrocaval ureter. Keywords: hydronephrosis, retrocaval ureter, neonate

Release of obstructing rectal cuff following transanal endorectal pullthrough for Hirschsprung’s disease: a laparoscopic approach

Obstructive problems secondary to a tight or a long rectal cuff following transanal endorectal pullthrough for Hirschsprung’s disease usually require redo surgery for release. Many approaches have been described. We describe the laparoscopic approach for the release of a tight or a long rectal cuff in two cases after a transanal endorectal pullthrough. Two patients had obstructive symptoms after transanal endorectal pullthrough for Hirschsprung’s disease. The first patient had a long rectal cuff that caused severe constipation with severe straining on defecation and the second patient had recurrence of symptoms with failure of spontaneous defecation with the need for an enema or a rectal tube for evacuation. A laparoscopic excision of the long rectal cuff was performed in the first patient and incision of the tight rectal cuff in the second patient. In both patients, the obstructing symptoms were because of a rectal cuff that was long in the first case and tight in the second. The procedure was completed laparoscopically with relief of symptoms and acquisition of normal defecation immediately after surgery. Approach of the rectal cuff was possible using laparoscopy and this technique facilitates release or excision of the rectal cuff when it causes obstructing symptoms without the need for extensive surgery and without the risk of causing fecal incontinence or wound disruption or infection using other more complicated techniques. Keywords: Hirschshprung, laparoscopy, obstruction, rectal cuf

Use of 2-Ethoxy(4H)-3,1-benzoxazin-4-one as a Precursor for Synthesis of Quinazoline and Quinazolinone Starting Materials

The interactions of 2-ethoxy(4H)-3,1-benzoxazin-4-one (1) with various nitrogen nucleophiles such as ammonium acetate,  hydrazine hydrate, ethanolamine, p-phenylenediamine, o-phenylenediamine, o-tolidine, dapsone, 2-aminophenol, 4-aminophenol, 4-aminobenzoic acid and 2-aminonicotinic acid have been discussed. The reactions of 2-thoxy-(3H)-quinazolin-4-one with ethyl chloroformate, phosphorus pentasulfide, chloroacetyl chloride and phosphorus oxychloride have also been investigated. Similar reactions of 2-ethoxy-4-chloroquinazoline with hydrazine hydrate and thiosemicarbazide have been introduced. Aminolysis of the 2-ethoxy group in some of the thiadiazoloquinazolinone derivatives has been attempted. The interactions of these aminolized derivatives and the 3-aminoquinazolinone with chloroacetyl chloride have been studied. All of the synthesized derivatives have been used in a wide range as starting materials for the synthesis of novel quinazoline and/or quinazolinones which have biological activity. The structures of all these products, obtained by heterocyclic ring opening and ring closure, were inferred by the IR, MS, 1H NMR spectral as well as elemental analyses. Keywords: Aminothiadiazole, Benzoxazin-4-one, N-nucleophile, quinazoline, quinazolin-4-one, thiosemicarbazide

Use of 2-{[5-(2-Amino-4-oxoquinazolin-3(4H)-yl)-1,3,4-thiadiazol-2-yl]methyl}-1H-isoindole-1,3(2H)-dione in the Synthesis of Novel Quinazolinone Derivatives

The 2-{[5-(2-Amino-4-oxoquinazolin-3(4H)-yl)-1,3,4-thiadiazol-2-yl]methyl}-1H-isoindole-1,3(2H)-dione 1 was synthesized and allowed to react with each of  p-methoxybenzaldehyde,  p-methoxyacetophenone and chloroacetyl chloride to produce the Schiff bases 2 and 3 and 2-chloro-N-(3-{5-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]-1,3,4-thiadiazol-2-yl}-4-oxo-3,4-dihydroquinazolin-2-yl)acetamide 6, respectively. The products 2 and 3 were reacted with phenyl isothiocyanate to afford 4 and 5. Derivative 6 was reacted with various nucleophiles, namely: thioglycolic acid, ethyl glycinate and 2-aminoethanol giving 7-9 respectively. In turn, the derivative 8 was reacted with α-bromoglucose tetraacetate affording product 8a whereas 9 was reacted with p-acetylaminobenzenesulfonyl chloride affording derivative 9a. Moreover, the reactions of the derivative 6 with potassium thiocyanate, potassium cyanate, malonitrile, ethyl cyanoacetate and ammonium acetate gave derivatives 10-15, respectively. All the synthesized derivatives were confirmed by the IR, mass, 1H-NMR and elemental analysis. Key words: Quinazolinyl thiazolidine, thioxodiazetidinyl quinazoline, piperazinyl quinazolinone, thiomorpholine and  triazinoquinazoline