Partial Flip Research Articles

Spin switching in room temperature spin reorientation transition process of Sm0.8Yb0.2FeO3 single crystal

We report that the introduction of a certain proportion of Yb ions into SmFeO3 single crystal can modulate the reduction of the spin reorientation (SR) transition temperature down to the room temperature region. Simultaneously, it maintains the spin configuration change between Γ2 (Cy, Gz, Fx) and Γ4 (Gx, Ay, Fz) and raises the magnetization compensation temperature of the single crystal. Both Zero-Field-Cooling (ZFC) and Field-Cooled-Cooling (FCC) modes along the a-axis are present with two type-I spin switching effects, which can be effectively regulated by the applied magnetic field. Interestingly, the type-II spin switching effect is observable along the c-axis in the ZFC mode under lower magnetic fields during the SR transition process at room temperature, an interesting magnetization phenomenon that is suppressed when the magnetic field is greater than 38 Oe. This type of spin switching effect arises from a partial flip of the moments of Sm3+. Additionally, the sharp spin switching induced by the magnetic field is also observed along the a- and c-axes with the variation of the magnetization with the applied magnetic field (M-H). This work is valuable for providing an insight into the magnetic coupling and competition between the two sublattices in the RFeO3 system and for facilitating the practical application of relevant spin switching materials.

Teaching Digital Signal Processing by Partial Flipping, Active Learning, and Visualization: Keeping Students Engaged With Blended Teaching

Effectiveness of teaching digital signal processing can be enhanced by reducing lecture time devoted to theory, and increasing emphasis on applications, programming aspects, visualization and intuitive understanding. An integrated approach to teaching requires instructors to simultaneously teach theory and its applications in storage and processing of audio, speech and biomedical signals. Student engagement can be enhanced by engaging students to work in groups during the class where students can solve short problems and short programming assignments or take quizzes. These approaches will increase student interest in learning the subject and student engagement.

Magnetic polydomain liquid crystal elastomers – synthesis and characterisation

ABSTRACT Although liquid crystal elastomers (LCE) are a fascinating class of materials with interesting thermomechanical properties of their own, the aim is to enhance their performance or add new features, e.g. response to external stimuli. The generally weak response of organic materials can be significantly intensified by mixing nano-sized magnetic particles into the host polymer matrix. An alternative approach is chemically coupling the nanoparticles to the elastomer. We achieved this by bonding functionalised magnetic nanoplatelets to the backbone of a main-chain LCE and obtained polydomain magnetic liquid crystal elastomers. We measured the magnetisation curves in samples, which were exposed to either small or large magnetic fields – their response being a consequence of partial particle reorientation or magnetic moment flipping. In contrast to the samples, which were exposed to small magnetic field and in which the remanent magnetisation can be reset to zero by heating the sample, the samples with flipped magnetisation within the platelets cannot be reversed into the original state. Coupling of magnetic and mechanical properties shows a slight magneto-elastic response at elevated temperatures and a significant inverse magneto-elastic effect: the magnetisation caused by mechanical stretching is almost equal to the magnetisation caused by an external magnetic field.

Effects of detailed geometry and real fluid thermodynamics on Spray G atomization

We present recent results toward the quantification of spray characteristics at engine conditions for an eight-hole counter-bored (stepped) GDI injector – Spray G in the ECN denomination. This computational study is characterized by two novel features: the detailed description of a real injector's internal surfaces via tomographic reconstruction; and a general equation of state that represents the thermodynamic properties of homogeneous liquid-vapor mixtures. The combined level-set moment-of-fluid approach, coupled to an embedded boundary formulation for moving solid walls, makes it possible to seamlessly connect the injector's internal flow to the spray. The Large Eddy Simulation (LES) discussed here presents evidence of partial hydraulic flipping and, during the closing transient, string cavitation. Results are validated by measurements of spray density profiles and droplet size distribution.

Effective Revisable Data Hiding in Encrypted Image for Protection of Image Content

In this article, we propose a reversible method for hiding data, in which the original image and hidden data can be restored on the receiving side. The owner encrypts the original image using an encryption key to protect the privacy of the image content. Each block of encrypted image is added to the little secret by Hider data using the key data hiding. Data hiding process causes only a small change in each partial pixel flip block, which improves decoded image visual quality. The image can be easily decoded receiver using the key, data encryption key to hide the adaptive soft characteristic of the evaluation function along the direction of the isophote, the secret data can be extracted from a decoded image and original image recovery can be restored more successfully.

Probing cholesterol binding and translocation in P-glycoprotein

P-glycoprotein (Pgp) is a biomedically important member of the ABC transporter superfamily that mediates multidrug resistance in various cancer types. Substrate binding and transport in Pgp are modulated by the presence of cholesterol in the membrane. Structural information on cholesterol binding sites and mechanistic details of its redistribution are, however, largely unknown. In this study, a set of 40 independent molecular dynamics (MD) simulations of Pgp embedded in cholesterol-rich lipid bilayers are reported, totaling 8 μs, enabling extensive sampling of cholesterol-protein interactions in Pgp. Clustering analyses of the ensemble of cholesterol molecules (∼5740) sampled around Pgp in these simulations reveal specific and asymmetric cholesterol-binding regions formed by the transmembrane (TM) helices TM1–6 and TM8. Notably, not all the putative cholesterol binding sites identified by MD can be predicted by the primary sequence based cholesterol-recognition amino acid consensus (CRAC) or inverted CRAC (CARC) motifs, an observation that we attribute to inadequacy of these motifs to account for binding sites formed by remote amino acids in the sequence that can still be spatially adjacent to each other. Binding of cholesterol to Pgp occurs more frequently through its rough β-face formed by the two protruding methyl groups, whereas the opposite smooth α-face prefers packing alongside the membrane lipids. One full and two partial cholesterol flipping events between the two leaflets of the bilayer mediated by the surface of Pgp are also captured in these simulations. All flipping events are observed in a region formed by helices TM1, TM2, and TM11, featuring two full and two partial CRAC/CARC motifs, with Tyr49 and Tyr126 identified as key residues interacting with cholesterol during this event. Our study is the first to report direct observation of unconventional cholesterol translocation on the surface of Pgp, providing a secondary transport model for the known flippase activity of ABC exporters of cholesterol.This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.

The impact of the flipped classroom in a principles of microeconomics course: evidence from a quasi-experiment with two flipped classroom designs

This study uses a quasi-experimental, non-equivalent group design to analyze the outcomes in terms of students’ learning and satisfaction of the redesign of a first-year, principles of microeconomics course from a lecture-based course using active learning techniques in 2013 to a partial flipped classroom in 2014 and a full flipped classroom in 2015.Students perceived a higher degree of achievement of the learning goals in both flipped courses compared to the non-flipped active learning course. Moreover, participating in the partial or full flipped classroom decreased the odds of a D or F grade or of withdraw. However, only the partial flip was associated with overall better learning outcomes in the final exam, while there was no statistically significant difference between the non-flipped active learning course and the full flip. Age was negatively associated with learning outcomes and increased the odds of a D or F grade or of withdraw. Gender had no statistically significant impact on learning outcomes. Students were least satisfied with the full flip and equally satisfied with the non-flipped active learning course and the partial flip. Lower satisfaction appears to be due to increased workload, which students evaluated to be highest in the full flip, as well as to elements of group work design. In the flipped classroom design, the pre-class multiple choice tests on Moodle emerged as a clear favorite in students’ teaching evaluations.

Twinning ferroelasticity facilitated by the partial flipping of phenyl rings in single crystals of 4,4'-dicarboxydiphenyl ether.

Evidence of ferroelasticity in a non-planar organic molecular crystal is presented for 4,4′-dicarboxydiphenyl ether. Ferroelasticity has been demonstrated by the micro- and macroscopic mechanical characterization of single crystals, including recording of a full hysteretic stress–strain cycle. The underlying mechanism involves the partial flipping of phenyl rings.

Direct Observation of Unidirectional Cholesterol Flipping on the Surface of P-Glycoprotein

P-glycoprotein (Pgp) is a biomedically important member of the largest superfamily of ABC transporters and mediates multidrug resistance in many cancer types. Substrate binding and transport in Pgp are modulated by the presence of cholesterol in the membrane, while cholesterol itself is a substrate and exported by Pgp. Structural information on cholesterol binding sites and mechanistic details of its transport pathway are largely unknown. In this study, a set of 35 independent simulations of Pgp oriented independently in cholesterol-rich lipid bilayers were performed, adding to a total of 7 μs, enabling extensive sampling of lipid-protein interactions. From the ensemble of cholesterol molecules (∼4700) sampled in these simulations, one complete and two partial cholesterol flipping events were captured. All of the flipping events visited a region formed by transmembrane (TM) helices TM1, TM2, and TM11 with Tyr 49 and Tyr 126 as key residues interacting with cholesterol. This region has been identified with two cholesterol-recognition amino acid sequence (CRAC) motifs. Cholesterol flipping from the inner leaflet initially binds to this motif and assumes a 90° angle to the membrane normal burying its only hydroxyl group within the surface of the protein followed by flipping to the outer leaflet. Convergence and clustering analyses of cholesterol molecules around Pgp revealed that cholesterol binds to specific regions formed between TM1-6 and TM8 helices interacting through its rough surface. From the generated ensemble of cholesterol sampling around Pgp, only a single complete cholesterol flipping from inner leaflet to outer leaflet has been directly observed, which supports the known flippase activity of Pgp. Our study is the first to report that substrate translocation by Pgp might take place through pathways on the surface of the protein.

A partial flip classroom exercise in a large introductory general biology course increases performance at multiple levels

Incorporation of active learning into large lecture classes is gaining popularity as a pedagogical method due to its known benefits in helping learning outcomes. A more recent active learning technique that has emerged is the flipped classroom. In this study, we investigated the effects of incorporating a ‘partial-flip’ into an introductory general biology course, where only a portion of the class time was spent in a flipped classroom format. This partial flip presented the classic biology experiment of Meselson and Stahl that discovered the mechanism of DNA replication. Performance on in-class formative assessments and subsequent summative assessments (eg out-of-class assignments and exams relating to this material) was compared between a class that had the partial flip and a control class that had a traditional lecture. The partial flip students scored higher on in-class formative questions, specific exam questions and final exam essay questions. We found that the partial flip had different effects in males versus females depending on the assessment. The partial flip manipulation appeared equally effective in aiding both below and above average students in formative assessments. Overall, this study shows that the partial flip classroom can be an effective technique to incorporate into existing courses and that it does provide some benefits compared to traditional lecture.

Partial Base Flipping Is Sufficient for Strand Slippage near DNA Duplex Termini

Strand slippage is a structural mechanism by which insertion-deletion (indel) mutations are introduced during replication by polymerases. Three-dimensional atomic-resolution structural pathways are still not known for the decades-old template slippage description. The dynamic nature of the process and the higher energy intermediates involved increase the difficulty of studying these processes experimentally. In the present study, restrained and unrestrained molecular dynamics simulations, carried out using multiple nucleic acid force fields, are used to demonstrate that partial base-flipping can be sufficient for strand slippage at DNA duplex termini. Such strand slippage can occur in either strand, i.e. near either the 3' or the 5' terminus of a DNA strand, which suggests that similar structural flipping mechanisms can cause both primer and template slippage. In the repetitive mutation hot-spot sequence studied, non-canonical base-pairing with exposed DNA groove atoms of a neighboring G:C base-pair stabilizes a partially flipped state of the cytosine. For its base-pair partner guanine, a similar partially flipped metastable intermediate was not detected, and the propensity for sustained slippage was also found to be lower. This illustrates that a relatively small metastable DNA structural distortion in polymerase active sites could allow single base insertion or deletion mutations to occur, and stringent DNA groove molecular recognition may be required to maintain intrinsic DNA polymerase fidelity. The implications of a close relationship between base-pair dissociation, base unstacking, and strand slippage are discussed in the context of sequence dependence of indel mutations.

Correction to “Black bone” MRI: a partial flip angle technique for radiation reduction in craniofacial imaging. Br J Radiol 2012;85: 272–8

Correction to “Black bone” MRI: a partial flip angle technique for radiation reduction in craniofacial imaging. Br J Radiol 2012;85: 272–8

“Black bone” MRI: a partial flip angle technique for radiation reduction in craniofacial imaging

The potential harmful effects of ionising radiation continue to be highlighted. Radiation reduction techniques have largely consisted of low-dose techniques rather than a shift to non-ionising methods of imaging. CT scanning is frequently employed for imaging the craniofacial skeleton despite being one of the key anatomical regions for radiation protection in view of the radiosensitive lens and thyroid gland. We describe a low flip angle gradient echo MRI sequence which provides high image contrast between bone and other tissues but reduces the contrast between individual soft tissues. This permits the "black bone" to be easily distinguished from the uniformity of the soft tissues. While maintaining a repetition time of 8.6 ms and an echo time of 4.2 ms, the flip angle which provided optimised suppression of both fat and water was identified to be 5°. The biometric accuracy of this sequence was confirmed using a phantom to obtain direct anatomical measurements and comparable CT scanning. The average discrepancy between black bone MRI measurements and direct anatomical measurements was 0.32 mm. Black bone MRI therefore has the potential to reduce radiation exposure by replacing CT scanning when imaging the facial skeleton, with particular scope for imaging benign conditions in the young.

Partial Single Base Flipping is Sufficient to Enable Strand Slippage at DNA Duplex Termini

DNA strand slippage is a structural mechanism by which mutations are introduced during replication by DNA polymerases. Although the template-slippage mechanism was suggested by Streisinger and coworkers around 40 years ago, there is no detailed atomic-resolution understanding of the dynamic pathways by which such strand slippage can occur. Using unrestrained molecular dynamics simulations, the present study demonstrates that partial single base flipping can be sufficient to enable spontaneous strand slippage at DNA duplex termini. The strand slippage was observed in both strands at the terminal end of a DNA duplex illustrating exactly how either insertion or deletion (indel) mutations were possible depending on which strand the partially flipped base belonged to. These findings highlight the steric and non-bonded interaction stringency required of DNA polymerase active sites to prevent indel mutations. This relationship between base flipping and strand slippage and its implications for sequence dependence of indel mutations will be discussed along with planned future studies to characterize these newly discovered dynamic DNA strand slippage pathways.

Black‐blood imaging of the human heart using rapid stimulated echo acquisition mode (STEAM) MRI

To develop a rapid stimulated echo acquisition mode (STEAM) MRI technique for "black-blood" imaging of the human heart that overcomes the single-slice limitation and partially compromised blood suppression associated with double inversion-recovery techniques. Black-blood multislice images of the heart along anatomic orientations and triggered to end diastole were obtained from healthy human subjects at 3T using rapid STEAM MRI sequences with five-eighths partial Fourier encoding and variable flip angles. Single-shot STEAM images at 2.5 x 2.5 mm2 in-plane resolution and 6-mm section thickness were recorded in 230 msec from individual heartbeats. Improved signal-to-noise ratio (SNR) and higher spatial resolution of 2.0 x 2.0 mm2 and 1.5 x 1.5 mm2 were achieved by segmented multishot STEAM MRI with interleaved k-space acquisitions (160 msec each) from several heartbeats. In a single breathhold covering 18 heartbeats selected applications employed either three segments with six sections or six segments with three sections. Because stimulated echoes (STEs) dephase signals from moving spins, rapid STEAM images are free from blood signal contamination. The method offers a flexible tradeoff between spatial resolution, imaging speed (i.e., number of segments), and volume coverage (i.e., number of sections). Rapid STEAM MRI of the heart emerges as a simple technique for multislice imaging of the myocardial wall with efficient flow suppression.

Energetics of the dipole flip-flop motion in a ferroelectric polymer chain

The authors report on a study of dipole flip-flop "local" transition in ferroelectric polyvinylidene fluoride [P(VDF)] chains, using total energy calculation based on the density functional theory. The calculated results indicate that a simple flipping of a single electric dipole moment is energetically allowed. Furthermore, such a flipping involves no change either in bond length, bond angle, or the orientation of the chain. The calculations also show that on a thin film of ordered chains, strong dipole interactions existing in P(VDF) could cause modulation of the dipole orientation thus forming superlattices on P(VDF) films. These results are in good agreement with recent scanning tunnel microscope experimental measurements. Furthermore, our calculations show that partial flipping may also exist and extend over a length of several monomers during the flip-flop transition.

Dissociative adsorption of NO upon Al(111): Orientation dependent charge transfer and chemisorption reaction dynamics

The dissociative and abstractive chemisorption dynamics of NO on Al(111) were studied. A higher sticking probability for the N end-on of NO onto Al(111) was measured. In contrast, Auger electron experiments reveal stepped surfaces to be oxygen rich at low coverage after exposure to NO. Density functional theory calculations show (i) a few angstroms from the surface, an N end-on first collision geometry results in electronic structures consistent with charge transfer; (ii) there is stabilization on the surface for N end-on or side-on orientations; (iii) dissociation is enhanced by a partial or full flip of the molecule.

Crossing intrinsic depolarizing resonances by varying a partial Siberian snake.

We recently forced a 140 MeV polarized proton beam to cross intrinsic depolarizing resonances by varying a partial Siberian snake's strength for different values of the vertical and horizontal betatron tunes ${\ensuremath{\nu}}_{y}$ and ${\ensuremath{\nu}}_{x}$. A weak second-order intrinsic resonance was observed in the ${\ensuremath{\nu}}_{x}$ sweep; moreover, an unexpected partial spin flip was found in the ${\ensuremath{\nu}}_{y}$ sweep. We also varied the snake ramp time to identify the ${\ensuremath{\nu}}_{y}$ and ${\ensuremath{\nu}}_{x}$ regions where the resonance crossings occurred during the snake variation; in these crossings the polarization partially deviated from Froissart-Stora behavior.

“Dolichoectatic” Intracranial Vertebrobasilar Dissecting Aneurysm

We report five patients with intracranial vertebrobasilar dissecting aneurysms, all of whom had ischemic symptoms. Angiographically, four of the five cases revealed distention and elongation of the vertebrobasilar artery like dolichoectasia and one irregular stenosis, the so-called "string sign". Magnetic resonance imaging disclosed all dolichoectatic dissecting lesions by demonstrating intimal flaps, double lumen, or subacute clot in the false lumen. We also present a successful demonstration of slow flow in the false lumen by gradient refocused magnetic resonance imaging scan with partial flip angle by the cardiac gating method. It is suggested that many of the classical "dolichoectasia" may include dissecting lesions.

Magnetic Resonance Imaging of the Temporomandibular Joint: Preliminary Evaluation of Partial Flip Angle Three-Dimensional Volume Acquisitions Against Conventional Single and Multiecho Pulse Sequences

The authors imaged 20 temporomandibular joints (TMJs) in 20 patients with high field surface coil magnetic resonance imaging, to compare the accuracy and the clinical utility of thin section partial flip angle (PFA) three dimensional (3D) volume acquisitions with T1-weighted images (T1WI), spin echo, multiecho, long TR/short and long TE images, PFA gradient recalled acquisition in the steady state (GRASS) images in the diagnosis of internal derangement of the TMJ. Pathological conditions demonstrated on imaging studies included disk derangement, joint effusion, and osteocartilaginous lesions, such as degenerative arthritis, osteoporosis, osteochondritis dissecans and early avascular necrosis of the mandibular condyle.