Total Loop Length Research Articles

Design of an electrically small printed square loop antenna for closely spaced Tx/Rx systems

AbstractA highly miniaturised electrically small square loop antenna has been designed for operation at 2.5 GHz. The antenna is loaded using a simple series combination of two lumped inductors and two interdigitated capacitors in order to realise inherent impedance matching at a given miniaturisation level with respect to a specified source impedance, without using any external matching network. The designed antenna has an overall size of 0.061λ0 × 0.061λ0, which is approximately 75.6% miniaturised in terms of total loop length and 94% miniaturised in terms of overall footprint. The designed antenna is fabricated and the corresponding impedance matching and radiation patterns are measured, which are found to be in reasonable agreement with their simulated counterparts. Moreover, an investigation with two closely spaced electrically small SLAs, one for transmitting and the other for receiving, is carried out in this work in pursuit of maximising the isolation, which plays a crucial role in the Tx/Rx systems.

Laparoscopic gastric bypass surgery with a single anastomosis: a comparative analysis of the metabolic and bariatric effects

Objective. To compare the results of the effect of long–loop, distal and mini–gastric bypass surgery with a single anastomosis on the loss of excess body weight, indicators of protein, lipid, carbohydrate metabolism, correction of metabolic syndrome and development of deficiency states after 36 months. Materials and methods. Patients with morbid obesity were divided into 3 groups: Group 1 – 25 patients who underwent long–loop gastric bypass with a biliopancreatic loop length of 200 cm; Group 2 – 25 patients who underwent mini–gastric bypass with a biliopancreatic loop length of 200 cm using laparoscopic access; Group 3 – 25 patients who underwent distal gastric bypass with a total loop length of 250 cm. Results. 36 months after the operation, the loss of excess body weight was (69 ± 1.1)% in group 1, (70.1 ± 1.3)% in group 2 and (72 ± 0.9)% in group 3; remission of dyslipidaemia was observed in 4 (80%) of 5 patients in group 1, 11 (84.6%) of 13 patients in group 2 and 7 (100%) of 7 patients in group 3; remission of type II diabetes mellitus – in 3 (75%) out of 4, 5 (83.3%) out of 6 and 6 (100%) out of 6 patients, respectively, complete remission of arterial hypertension – in 6 (46.2%) out of 13, 7 (50%) out of 14 and 9 (60%) out of 15 patients, respectively. Conclusions. Laparoscopic long–loop gastric bypass with a single anastomosis is effective and safe, does not cause severe deficiency states, and can be used as a primary bariatric surgery.

Frequency pulling effect of an intraloop atomic filter in an optoelectronic oscillator.

The frequency pulling effect in an optoelectronic oscillator (OEO) due to the high dispersion produced by coherent population trapping (CPT) resonance in an intraloop Rb85 cell has been experimentally measured. With the direct modulation of the injection current of an extended-cavity diode laser, we construct the OEO and a beating signal with a frequency of 3.036GHz is filtered by CPT resonance. The effective total loop length of the OEO under the CPT resonance condition can be significantly increased. As the optical path length of the OEO is changed, the microwave-frequency shift of the OEO corresponding to the effective total loop length is measured and reported.

Dual Loop Optoelectronic Oscillator with Acousto-Optic Delay Line

A dual loop optoelectronic oscillator (OEO) based on an acousto-optic modulator (AOM) for single mode operation with an acousto-optic delay line is demonstrated in this paper. When the OEO operates, the free spectral range is a function of the total loop length of the OEO, which is mainly dependent on the propagation time of the acoustic wave in the AOM. Due to the huge difference in the magnitude between the speed of light and the acoustic velocity in the AOM, the effective loop length converted to light-propagation length of the OEO increases to 3.8 km. With 150 MHz oscillation frequency, phase noise of -118 dBc/Hz at 10 kHz frequency offset, and -140 dBc/Hz at 200 kHz frequency offset, is achieved.

Optoelectronic oscillator for a measurement of acoustic velocity in acousto-optic device.

We report a novel means of measuring the acoustic velocity based on a well-known acousto-optic interaction. With an acousto-optic modulator (AOM), we construct an optoelectronic oscillator (OEO) that can measure the acoustic velocity in the AOM directly. The free spectral range between the modes is a function of the total loop length of the OEO, which is mainly dependent on the propagation time of the acoustic wave through the AOM. By changing the propagation time, we measured the acoustic velocity from the variation of the free spectral range. The results are reported and compared with earlier results. This method is insensitive to the variation of the optical phase shift. In addition, the high frequency-stability and microwave spectral purity of the OEO allow reliable and precise measurements.

How long is too long? Effects of loop size on G-quadruplex stability

We compared here 80 different sequences containing four tracts of three guanines with loops of variable length (between 1 and 15 bases for unmodified sequences, up to 30 for fluorescently labeled oligonucleotides). All sequences were capable of forming stable quadruplexes, with Tm above physiological temperature in most cases. Unsurprisingly, the melting temperature was systematically lower in sodium than in potassium but the difference between both ionic conditions varied between 1 and >39°C (average difference: 18.3°C). Depending on the sequence context, and especially for G4 sequences involving two very short loops, the third one may be very long without compromising the stability of the quadruplex. A strong inverse correlation between total loop length and Tm was found in K+: each added base leads to a 2°C drop in Tm or ∼0.3 kcal/mol loss in ΔG°. The trend was less clear in Na+, with a longer than expected optimal loop length (up to 5 nt). This study will therefore extend the sequence repertoire of quadruplex-prone sequences, arguing for a modification of the widely used consensus (maximal loop size of 7 bases).

Stability and Molecular Recognition of Quadruplexes with Different Loop Length in the Absence and Presence of Molecular Crowding Agents

G-quadruplexes are known to be potential targets for therapeutic intervention, thus resulting in development of various quadruplex interacting ligands. However, until now, no systemic study has been performed to understand molecular recognition of quadruplex in the presence of molecular crowding agents mimicking cellular conditions. The stability and molecular recognition of quadruplex can be influenced by loop length. Herein, we attempted to study the interaction of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine (TMPyP4), a well-known G-quadruplex binding ligand with various DNA quadruplexes differing in total loop length and loop arrangement in both the absence and presence of molecular crowding agents. Results obtained from CD studies revealed that longer loops favor mixed and antiparallel conformation in both the absence and presence of 30% ethylene glycol. UV thermal melting studies revealed that the stability and formation of quadruplex increases in the presence of 30% ethylene glycol. Moreover, the binding of TMPyP4 molecule to both of the binding sites in different quadruplexes with total loop length varying from 3 to 9 remains unchanged in both the absence and presence of 30% ethylene glycol. The binding affinity (K(a)) of TMPyP4 was found to be decreased approximately by 1 order for the quadruplex sequences with total loop length varying from 11 to 15 in the presence of molecular crowding agents.

Carbon dioxide as a secondary fluid in natural circulation loops

In recent years there is growing interest in the use of carbon dioxide as a secondary fluid in various cooling and heating applications. In the present work a comparative study is made between carbon dioxide and conventional secondary fluids that can be used in natural circulation loops for various refrigeration and air conditioning applications. For the same heat input and total loop length, the results are presented in terms of the ratios of pipe diameter required when a conventional fluid is used to the required pipe diameter with carbon dioxide as the secondary fluid. Results are presented for both laminar and turbulent flow conditions. It is observed that due to its excellent thermo-physical and transport properties and near critical point operation, carbon dioxide gives rise to very compact systems when compared to most of the conventional secondary fluids. The difference in size is much greater for laminar flow conditions compared to turbulent flow conditions. Also, for a given system size, the temperature rise/drop across the heat exchangers is much smaller in case of carbon dioxide in comparison to other fluids.

A thermodynamic overview of naturally occurring intramolecular DNA quadruplexes

Loop length and its composition are important for the structural and functional versatility of quadruplexes. To date studies on the loops have mainly concerned model sequences compared with naturally occurring quadruplex sequences which have diverse loop lengths and compositions. Herein, we have characterized 36 quadruplex-forming sequences from the promoter regions of various proto-oncogenes using CD, UV and native gel electrophoresis. We examined folding topologies and determined the thermodynamic profile for quadruplexes varying in total loop length (5–18 bases) and composition. We found that naturally occurring quadruplexes have variable thermodynamic stabilities (ΔG37) ranging from −1.7 to −15.6 kcal/mol. Overall, our results suggest that both loop length and its composition affect quadruplex structure and thermodynamics, thus making it difficult to draw generalized correlations between loop length and thermodynamic stability. Additionally, we compared the thermodynamic stability of quadruplexes and their respective duplexes to understand quadruplex–duplex competition. Our findings invoke a discussion on whether biological function is associated with quadruplexes with lower thermodynamic stability which undergo facile formation and disruption, or by quadruplexes with high thermodynamic stability.

Discrete state model and accurate estimation of loop entropy of RNA secondary structures

Conformational entropy makes important contribution to the stability and folding of RNA molecule, but it is challenging to either measure or compute conformational entropy associated with long loops. We develop optimized discrete k-state models of RNA backbone based on known RNA structures for computing entropy of loops, which are modeled as self-avoiding walks. To estimate entropy of hairpin, bulge, internal loop, and multibranch loop of long length (up to 50), we develop an efficient sampling method based on the sequential Monte Carlo principle. Our method considers excluded volume effect. It is general and can be applied to calculating entropy of loops with longer length and arbitrary complexity. For loops of short length, our results are in good agreement with a recent theoretical model and experimental measurement. For long loops, our estimated entropy of hairpin loops is in excellent agreement with the Jacobson-Stockmayer extrapolation model. However, for bulge loops and more complex secondary structures such as internal and multibranch loops, we find that the Jacobson-Stockmayer extrapolation model has large errors. Based on estimated entropy, we have developed empirical formulae for accurate calculation of entropy of long loops in different secondary structures. Our study on the effect of asymmetric size of loops suggest that loop entropy of internal loops is largely determined by the total loop length, and is only marginally affected by the asymmetric size of the two loops. Our finding suggests that the significant asymmetric effects of loop length in internal loops measured by experiments are likely to be partially enthalpic. Our method can be applied to develop improved energy parameters important for studying RNA stability and folding, and for predicting RNA secondary and tertiary structures. The discrete model and the program used to calculate loop entropy can be downloaded at http://gila.bioengr.uic.edu/resources/RNA.html.

Conformational entropy of a pseudoknot polymer

The thermodynamics and kinetics of ABAB pseudoknot formation owing to reversible intrachain reactions are investigated for a flexible polymer based on the off-lattice Monte Carlo simulations. The polymer is made of N hard spheres tethered by inextensible bonds and consists of two reactive pairs AA and BB with binding energies -epsilon1 and -epsilon2, respectively, and three loop lengths (l1, l2, and l3). Although two intermediate states, loops A and B, may be formed, the folding path goes mainly through the intermediate loop whose free energy reduction associated with coil-to-loop crossover is greater. The conformational entropy loss is found to follow DeltaS=alpha ln N+G, where alpha approximately 2.48 for coil-loop crossover and alpha approximately 2.43 for loop-pseudoknot crossover. The constant G depends on the three loop lengths and the two end-to-reactive site lengths (L1 and L2). For a given total loop length, G is maximum when the three loop lengths are equal (l1=l2=l3). When l1=l3, the entropy loss is minimum if l2=0. However, the condition l1 not equal l3 makes G even smaller. This consequence indicates that asymmetry in loop lengths is thermodynamically favorable and this fact is consistent with observations of pseudoknotted RNA structures.

Dynamics of solar coronal loops

Observations in X-ray and EUV of the solar corona reveal the existence of very complex and dynamic structures made of plasma magnetically confined in loops. These structures can be studied by means of one-dimensional hydrodynamical loop models. Here we use a Lagrangian-remap code to simulate the dynamics of solar coronal loops with the purpose of quantifying the effects of varying the initial distribution of energy along the loop, the amount of input heating ( h 0 ), the total loop length ($2L$) and including/excluding the solar gravity term. In particular, the model calculations with no gravity are compared with the results obtained from previous isobaric, time-dependent models. Using a heat function that depends on distance along the loop and temperatures at the base of the loop typical of the solar corona, we find that in the non-gravity cases the plasma is allowed to cool down to chromospheric temperatures only when the decay length of the heating is below a certain critical value ($s_{H}/L=0.043$). For the same initial parameters, the inclusion of gravity produces final equilibrium states which are considerably hotter than those obtained when gravity is neglected and lowers the critical value of the decay length of the heating for which a cool condensation forms. In all cases, the outcome of the evolution can be predicted by a diagnostic diagram which describes the location of possible solutions for thermal equilibrium models.

Functional morphology of the avian medullary cone.

The organization of the renal medulla of the Gambel's quail, Callipepla gambelii, kidney was examined to determine the number of loops of Henle and collecting ducts and the surface area occupied by the different nephron segments as a function of distance down the medullary cones. Eleven medullary cones were dissected from the kidneys of four birds, and the tissue was processed and sectioned for light microscopy. In addition, individual nephrons were isolated on which total loop thin descending segment and thick prebend segment lengths were measured. The results show no correlation between the absolute number of loops of Henle and the length of the medullary cones. The number of thick and thin limbs of Henle and collecting ducts decrease exponentially with distance toward the apex of the cones and the rate of decrease is similar for cones of different lengths. Initially there is a rapid decrease in the number of thin limbs of Henle, indicating that most nephrons do not penetrate the cones a great distance. Thick descending limbs of Henle (prebend segment) ranged in length from 50 to 770 microm, and there was little correlation with the total length of the loop of Henle. However, the length of the thin limb of Henle correlated well with total loop length. The cell surface areas of the limbs of the loop of Henle and the collecting ducts decreased toward the apex of the cones.

Rotation measurement with the use of a pulsed Er-doped fiber laser with integrated optic circuit: Proposal, simple theory, and experiment

We propose a noel pulsed fiber laser rotation sensor with a LiNbO integrated optic circuit, Sagnac fiber loop, Er-doped fiber, and 3 semiconductor pumping lasers. A simple analysis is completed and the output equation is deried. Theariance of the output pulse when rotation occurs is also analyzed. In addition, we also conducted a related experiment for rotation measurement. When the gain of the fiber ampli- fier is oer the round-trip loss and the phase modulation frequency satisfies the total round-trip time, this optical system produces the laser emission in a pulse state. The rotation rate is measured from the shift of the peak position of the output pulse. It is shown that the resolution of rotation measurement increases if we use a smaller phase modulation depth. But the sharpness of the optical pulse must be maintained by () reducing the losses or increasing the gain of optical amplifier in the whole optical system. Q 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 311)315, 1997. laser modes 6 . In this research we propose a novel fiber-optic rotation sensor with an integrated optic circuit, a Sagnac fiber loop, and an Er-doped fiber amplifier. This optical system produces a laser emission in the pulse state if the gain of fiber amplifier is greater than the whole round-trip transmis- sion loss, and if the frequency of phase modulator and the total loop length satisfy a certain mode-lock condition. The measurement of rotation rate is based on the peak shift of output pulse induced by the Sagnac effect.

An ultrasonic fiber-optic hydrophone incorporating a push-pull transducer in a Sagnac interferometer

A theoretical and experimental analysis of a push-pull acoustic transducer incorporated in a Sagnac interferometer is presented. The transducer is optimized for detection of ultrasonic signals in the frequency range 0.4-1.5 MHz. Two different configurations are investigated. In one, the sensing fiber forming the transducer constitutes the total loop length, and in the second an additional delay coil is included in the middle section of the Sagnac loop. In the latter we demonstrate experimentally noise-equivalent pressures of 36-43 dB re. 1 /spl mu/Pa/Hz/sup 1/2/ in the frequency range 0.4-1.0 MHz. An approximate theoretical model is presented, and we obtain reasonable agreement between theory and experiment for both the frequency-dependent noise equivalent pressure and the directional responsivity of this push-pull acoustic fiber-optic sensor. >