Loop Arm Research Articles

Molecular dynamics simulations of cognate and non-cognate AspRS-tRNAAsp complexes

Aspartyl tRNA synthetase (AspRS), one of the 20 aminoacyl-tRNA synthetases, plays an important role in protein synthesis by catalyzing the aminoacylation reaction and synthesises Aspartyl-tRNA (tRNAAsp). A typical three-dimensional structure of AspRS comprises three distinct domains for the recognition of cognate tRNA and catalysis, namely, anti-codon binding domain/N-terminal domain, hinge domain and catalytic domain through their interactions with anti-codon loop, D-stem and acceptor arm of cognate tRNA, respectively. In this work, we have studied the structural characteristics of each domain of AspRS to understand the recognition mechanism of tRNAAsp using molecular dynamics simulations. The dynamics of AspRS-tRNAAsp complexes from E.coli (cognate and non-cognate), S.cerevisiae (cognate) and T.thermophilus (non-cognate) were compared to understand the differences in recognition of cognate and non-cognate tRNAs. Our results explain that the conformational changes associated with the recognition of tRNA occur only in the cognate complexes. Among the cognate complexes, the conformational changes in yeast AspRS are highly controlled during tRNAAsp recognition than that of in the E. coli AspRS. Moreover, the functional motions required for the tRNA recognition are observed only in the cognate complexes, and the conformational changes in AspRS and their recognition of tRNAAsp are organism specific.Communicated by Ramaswamy H. Sarma

My Team of Care Study: A Pilot Randomized Controlled Trial of a Web-Based Communication Tool for Collaborative Care in Patients With Advanced Cancer.

BackgroundThe management of patients with complex care needs requires the expertise of health care providers from multiple settings and specialties. As such, there is a need for cross-setting, cross-disciplinary solutions that address deficits in communication and continuity of care. We have developed a Web-based tool for clinical collaboration, called Loop, which assembles the patient and care team in a virtual space for the purpose of facilitating communication around care management.ObjectiveThe objectives of this pilot study were to evaluate the feasibility of integrating a tool like Loop into current care practices and to capture preliminary measures of the effect of Loop on continuity of care, quality of care, symptom distress, and health care utilization.MethodsWe conducted an open-label pilot cluster randomized controlled trial allocating patients with advanced cancer (defined as stage III or IV disease) with ≥3 months prognosis, their participating health care team and caregivers to receive either the Loop intervention or usual care. Outcome data were collected from patients on a monthly basis for 3 months. Trial feasibility was measured with rate of uptake, as well as recruitment and system usage. The Picker Continuity of Care subscale, Palliative care Outcomes Scale, Edmonton Symptom Assessment Scale, and Ambulatory and Home Care Record were patient self-reported measures of continuity of care, quality of care, symptom distress, and health services utilization, respectively. We conducted a content analysis of messages posted on Loop to understand how the system was used.ResultsNineteen physicians (oncologists or palliative care physicians) were randomized to the intervention or control arms. One hundred twenty-seven of their patients with advanced cancer were approached and 48 patients enrolled. Of 24 patients in the intervention arm, 20 (83.3%) registered onto Loop. In the intervention and control arms, 12 and 11 patients completed three months of follow-up, respectively. A mean of 1.2 (range: 0 to 4) additional healthcare providers with an average total of 3 healthcare providers participated per team. An unadjusted between-arm increase of +11.4 was observed on the Picker scale in favor of the intervention arm. Other measures showed negligible changes. Loop was primarily used for medical care management, symptom reporting, and appointment coordination.ConclusionsThe results of this study show that implementation of Loop was feasible. It provides useful information for planning future studies further examining effectiveness and team collaboration. Numerically higher scores were observed for the Loop arm relative to the control arm with respect to continuity of care. Future work is required to understand the incentives and barriers to participation so that the implementation of tools like Loop can be optimized.Trial RegistrationClinicalTrials.gov NCT02372994; https://clinicaltrials.gov/ct2/show/NCT02372994 (Archived by WebCite at http://www.webcitation.org/6r00L4Skb).

Triband Metaloop Antenna

The radiation from a conventional metamaterial loop antenna, designated as the reference metaloop (REF), is circularly polarized (CP) within two frequency bands. This letter presents a new metaloop antenna (STUBL), where stubs are added to the loop arm. Analysis reveals that the radiation from the STUBL is CP within three frequency bands. The gain of the STUBL is compared to that of the REF. The theoretical radiation pattern and VSWR of the STUBL are also presented with experimental results.

A Novel Ultrawideband Exponentially Tapered Slot Antenna of Combined Electric-Magnetic Type

A novel exponentially tapered slot antenna with ultrawide bandwidth and small late-time ring is presented. A microstrip-to-coplanar-stripline (CPS) transition of Chebyshev multisection type is used as feeding transmission. The exponentially tapered slot, which is considered as electric-type radiator (ER), is combined with a magnetic-type radiator (MR) to achieve ultrawideband performance and small size. The MR is completed by a lumped resistor bridged between the loop arm and the transmission ground. The measured impedance bandwidth (VSWR <; 2) of optimized antenna is 0.65 ~ 5.9 GHz, which agrees well with the simulated results. The measured gain is almost 3 dBi in the whole band, and the front-to-back ratio is about 15 dB.

YBa2Cu3O7−δ nanorings to probe fluxoid quantization in High Critical Temperature Superconductors

We have realized YBa2Cu3O7−δ (YBCO) nanorings and measured the magnetoresistance R(B) close to the superconducting transition. The large oscillations that we have measured can be interpreted in terms of vortex dynamics triggering the nanowires to the resistive state. The Fast Fourier Transform spectrum of the magnetoresistance oscillations shows a single sharp peak for nanorings with narrower loop arm width: this peak can be univocally associated to a h/2e periodicity as predicted for optimally doped YBCO. Moreover it is a clear evidence of a uniform vorticity of the order parameter inside the rings, confirming a high degree of homogeneity of our nanostructures. This result gives a boost to further investigations of YBCO nanorings at different dopings within the superconducting dome, where in the underdoped regime a R(B) periodicity different from the conventional h/2e has been predicted.

Midterm experience of ipsilateral axillary-axillary arteriovenous loop graft as tertiary access for haemodialysis.

Objectives. To present a series of ipsilateral axillary artery to axillary vein loop arm grafts as an alternative vascular access procedure for haemodialysis in patients with difficult access. Design. Retrospective case series. Methods. Patients who underwent an axillary loop arteriovenous graft from September 2009 to September 2012 were included. Preoperative venous imaging to exclude central venous stenosis and to image arm/axillary veins was performed. A cuffed PTFE graft was anastomosed to the distal axillary artery and axillary vein and looped on the arm. Results. 25 procedures were performed on 22 patients. Median age was 51 years, with 9 males and 13 females. Median number of previous access procedures was 3 (range 0–7). Median followup was 16.4 months (range 1–35). At 3 months and 1 year, the primary and secondary patency rates were 70% and 72% and 36% and 37%, respectively. There were 11 radiological interventions in 6 grafts including 5 angioplasties and 6 thrombectomies. There were 19 surgical procedures in 10 grafts, including thrombectomy, revision, repair for bleeding, and excision. Conclusions. Our series demonstrates that the axillary loop arm graft yields acceptable early patency rates in a complex group of patients but to maintain graft patency required high rates of surgical and radiological intervention, in particular graft thrombectomy.

Radiation Characteristics of a Metaloop Antenna

A dual-band counter-circularly polarized (CP) square loop antenna is investigated. This loop antenna has a single feed point, and the loop arm is composed of numerous segments with capacitive and inductive elements that generate a negative phase constant. When the loop is wound in the counterclockwise direction from the feed point, a left-handed (LH) CP wave is obtained below the balanced frequency (3 GHz), and a right-handed (RH) CP wave is obtained above the balanced frequency. Such counter CP radiation cannot be obtained using a conventional single-feed loop antenna. The LHCP and RHCP radiation patterns are compared, and the frequency bandwidths for the axial ratio and gain are revealed. The VSWR within these CP radiation bands is small, as desired. The experimental results validate the theoretical results.

Trinucleotide Repeat DNA Alters Structure To Minimize the Thermodynamic Impact of 8-Oxo-7,8-dihydroguanine

In the phenomenon of trinucleotide repeat (TNR) expansion, an important interplay exists between DNA damage repair of 8-oxo-7,8-dihydroguanine (8-oxoG) and noncanonical structure formation. We show that TNR DNA adapts its structure to accommodate 8-oxoG. Using chemical probe analysis, we find that CAG repeats composing the stem-loop arm of a three-way junction alter the population of structures in response to 8-oxoG by positioning the lesion at or near the loop. Furthermore, we find that oligonucleotides composed of odd-numbered repeat sequences, which form populations of two structures, will also alter their structure to place 8-oxoG in the loop. However, sequences with an even number of repeats do not display this behavior. Analysis by differential scanning calorimetry indicates that when the lesion is located within the loop, there are no significant changes to the thermodynamic parameters as compared to the DNA lacking 8-oxoG. This contrasts with the enthalpic destabilization observed when 8-oxoG is base-paired to C and indicates that positioning 8-oxoG in the loop avoids the thermodynamic penalty associated with 8-oxoG base-pairing. Since formation of stem-loop hairpins is proposed to facilitate TNR expansion, these results highlight the importance of defining the structural consequences of DNA damage.

Polarization controlled tunable multiwavelength SOA-fiber laser based on few-mode polarization maintaining fiber loop mirror

A tunable multiwavelength fiber ring laser based on a semiconductor optical amplifier and few-mode polarization maintaining fiber (FM-PMF) loop mirror is proposed and experimentally demonstrated. It is accomplished by simply adjusting a polarization controller (PC) next to the FM-PMF in the loop arm for the polarization-dependent mode excitation in the FM-PMF and the resulting effective refractive index change. In addition, the undesirable dependence of the transmission loss of the FM-PMF loop mirror on the rotation angle of the PC in the loop arm can be reduced by using a fiber coupler with unequal coupling ratio instead of equal coupling ratio. Stable and tunable multiwavelength operation with up to 11 lasing lines at about 1.5 nm interval is achieved with the power deviation less than 2 dB and optical signal to noise extinction ratio over 35 dB.

Switchable and Tunable Dual-Line Erbium-Doped Fiber Ring Laser in the $C$- Plus $L$-Band Based on Merged Interference Effects

A simple but novel concept of switchable and tunable dual-line erbium-doped fiber ring laser in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> - plus <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -band is proposed and demonstrated. It is based on concurrence of the Sagnac and modal interferences in a fiber loop mirror including cascaded high birefringence few-mode fiber (HB-FMF) and polarization controller (PC). Random combination of the two lasing lines, one in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band and the other in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -band, can be realized by adjusting only the PC next to the HB-FMF in the loop arm. In addition, they can be simultaneously tuned at a discrete step equal to the channel spacing of the modal interference. The output power flatness is better than ±0.5 dB for both the single- and dual-line emissions by carefully choosing the HB-FMF length with the 3-dB spectral linewidth narrower than 0.03 nm and signal-to-noise extinction ratio higher than 40 dB during the whole switching and tuning processes.

Broadly Tunable Fiber Laser Based on Merged Sagnac and Intermodal Interferences in Few-Mode High-Birefringence Fiber Loop Mirror

A broadly tunable fiber ring laser including a few-mode high-birefringence fiber (FM-HBF) loop mirror is proposed and demonstrated. The operation mechanism is based on simultaneous occurrence of Sagnac and intermodal interferences in the FM-HBF loop mirror and polarization dependence of the modal excitation in the FM-HBF. While adjusting only a polarization controller next to the FM-HBF in the loop arm, the lasing wavelength can be tuned at a discrete step defined by the intermodal interference. The tunable range exceeding 40 nm with sidemode suppression ratio over 40 dB and power uniformity better than 1 dB at a discrete step of about 2.2 nm has been successfully demonstrated for the proposed fiber ring laser.

On false lock in suppressed carrier MPSK tracking loops

The problem of false lock in suppressed-carrier minimum phase-shift keying (MPSK) tracking loops (M>4 in particular), such as Mth power phase-locked loop (PLL) and MPSK Costas loop carrier recovery subsystems, is investigated. It is demonstrated that such tracking loops false lock onto the received signal when the received carrier frequency and the reference signal frequency generated by MPSK tracking loops are mismatched by multiples of 1/M of the MPSK symbol rate. False lock margins (FLMs) for the suppressed carrier MPSK tracking loops are obtained for a noiseless system model as well as for a model corrupted by additive white Gaussian noise (AWGN). Numerical results are presented in order to explain the influence of system parameters, such as the time-bandwidth product of MPSK Costas loop arm filters (or the Mth power PLL prefilter), arm filters' output signal-to-noise ratio and the input signal-to-noise ratio, on the performance of MPSK tracking loops.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Vascular access grafts for chemotherapy. Use in forty patients at M. D. Anderson Hospital.

Forty-two arteriovenous grafts were placed to provide vascular access in 40 patients with poor or sclerosed superficial veins. Thirty-nine patients had malignant disease and required chemotherapy, while one patient with aplastic anemia needed frequent transfusions. Thirty-two grafts were placed in the arm (27 straight and 5 loop), and ten in the leg (femoral-femoral loop). Thirty-seven shunts consisted of 6 mm polytetrafluoroethylene (PTFE), and five were 6 mm Dacron((R)). The straight brachial artery to axillary vein PTFE graft was preferred, while the PTFE femoral loop graft was a satisfactory alternative. The loop arm graft was associated with a high complication rate and is no longer used. Local anesthesia was employed in all cases except for a 3-year-old child. There was no operative mortality and no severe morbidity, despite subsequent myelosuppression by chemotherapeutic agents injected via these grafts. Thirty patients are alive, while ten died of their malignancy. Twenty-six grafts are functional and have been in place an average 4.4 months (range: 1 to 14 mo.). Acceptance by patients and particularly by personnel in the out-patient chemotherapy unit has been enthusiastic. Vascular access grafts can be inserted safely and provide a convenient route for drawing blood samples, and for administering chemotherapy and intermittent intravenous therapy in selected patients with neoplastic disease.

On the Calculation of Squaring Loss in Costas Loops with Arbitrary Arm Filters

The calculation of the optimum performance of suppressed carrier receivers with Costas loop tracking is directly related to evaluating the loop's so-called squaring loss. Recent work by the author and others presented specific numerical results for this loss when the input data were biphase- L (Manchester coded) and the Costas loop arm filters were of the n -pole Butterworth type. These results were largely obtained by numerical integration on a digital computer. This paper presents a partial fraction expansion technique for arriving at closed form expressions for squaring loss for Costas loops with arbitary arm filters and NRZ as well as Manchester coded data. Specific closed form results are given for one and two pole Butterworth filters as examples.

Optimum Performance of Suppressed Carrier Receivers with Costas Loop Tracking

The performance of suppressed carrier receivers with Costas loop tracking is optimized by proper choice of loop arm filter bandwidth. In particular, it is shown that for a variety of passive arm filter types, there exists, for a given data rate and data signal-signal-to-noise ratio, an optimum filter bandwidth in the sense of minimizing the loop's squaring loss. For the linear theory case, this is equivalent to minimizing the loop's tracking jitter. When symbol synchronization is known, it is shown that by replacing the passive arm filters with active filters, i.e., integrate-and-dump circuits, one can achieve an improvement in carrier-to-noise ratio of as much as 4 to 6 dB depending on the passive arm filter type used for comparison and the value of data signal-to-noise ratio (SNR).