Unique Geometric Features Research Articles

Regional deposition of particles in an image-based airway model: large-eddy simulation and left-right lung ventilation asymmetry.

Regional deposition and ventilation of particles by generation, lobe and lung during steady inhalation in a computed tomography (CT) based human airway model are investigated numerically. The airway model consists of a seven-generation human airway tree, with oral cavity, pharynx and larynx. The turbulent flow in the upper respiratory tract is simulated by large-eddy simulation. The flow boundary conditions at the peripheral airways are derived from CT images at two lung volumes to produce physiologically-realistic regional ventilation. Particles with diameter equal to or greater than 2.5 microns are selected for study because smaller particles tend to penetrate to the more distal parts of the lung. The current generational particle deposition efficiencies agree well with existing measurement data. Generational deposition efficiencies exhibit similar dependence on particle Stokes number regardless of generation, whereas deposition and ventilation efficiencies vary by lobe and lung, depending on airway morphology and airflow ventilation. In particular, regardless of particle size, the left lung receives a greater proportion of the particle bolus as compared to the right lung in spite of greater flow ventilation to the right lung. This observation is supported by the left-right lung asymmetry of particle ventilation observed in medical imaging. It is found that the particle-laden turbulent laryngeal jet flow, coupled with the unique geometrical features of the airway, causes a disproportionate amount of particles to enter the left lung.

Chromophore-functionalized dendrimers for sensing applications

Chromophore-functionalized dendrimer sensors represent a new class of highly sensitive sensing materials. Here we review various strategies regarding dendrimer sensors, with specific attention being paid to how to achieve signal amplification using dendrimers’ unique geometric features.

Computationally Designed Families of Flat, Tubular, and Cage Molecules Assembled with “Starbenzene” Building Blocks through Hydrogen‐Bridge Bonds

Using density functional calculations, we demonstrate that the planarity of the nonclassical planar tetracoordinate carbon (ptC) arrangement can be utilized to construct new families of flat, tubular, and cage molecules which are geometrically akin to graphenes, carbon nanotubes, and fullerenes but have fundamentally different chemical bonds. These molecules are assembled with a single type of hexagonal blocks called starbenzene (D(6h) C(6)Be(6)H(6)) through hydrogen-bridge bonds that have an average bonding energy of 25.4-33.1 kcal mol(-1). Starbenzene is an aromatic molecule with six pi electrons, but its carbon atoms prefer ptC arrangements rather than the planar trigonal sp(2) arrangements like those in benzene. Various stability assessments indicate their excellent stabilities for experimental realization. For example, one starbenzene unit in an infinite two-dimensional molecular sheet lies on average 154.1 kcal mol(-1) below three isolated linear C(2)Be(2)H(2) (global minimum) monomers. This value is close to the energy lowering of 157.4 kcal mol(-1) of benzene relative to three acetylene molecules. The ptC bonding in starbenzene can be extended to give new series of starlike monocyclic aromatic molecules (D(4h) C(4)Be(4)H(4)(2-), D(5h) C(5)Be(5)H(5)(-), D(6h) C(6)Be(6)H(6), D(7h) C(7)Be(7)H(7)(+), D(8h) C(8)Be(8)H(8)(2-), and D(9h) C(9)Be(9)H(9)(-)), known as starenes. The starene isomers with classical trigonal carbon sp(2) bonding are all less stable than the corresponding starlike starenes. Similarly, lithiated C(5)Be(5)H(5) can be assembled into a C(60)-like molecule. The chemical bonding involved in the title molecules includes aromaticity, ptC arrangements, hydrogen-bridge bonds, ionic bonds, and covalent bonds, which, along with their unique geometric features, may result in new applications.

Creation of a standardized geometry of the human nasal cavity

A novel, standardized geometry of the human nasal cavity was created by aligning and processing 30 sets of computed tomography (CT) scans of nasal airways of healthy subjects. Digital three-dimensional (3-D) geometries of the 60 single human nasal cavities (30 right and 30 mirrored left cavities) were generated from the CT scans and measurements of physical parameters of each single nasal cavity were performed. A methodology was developed to scale, orient, and align the nasal geometries, after which 2-D digital coronal cross-sectional slices were generated. With the use of an innovative image processing algorithm, median cross-sectional geometries were created to match median physical parameters while retaining the unique geometric features of the human nasal cavity. From these idealized 2-D images, an original 3-D standardized median human nasal cavity was created. This new standardized geometry was compared against the original geometries of all subjects as well as limited existing data from the literature. The new model has potential for use as a geometric standard in future experimental and numerical studies of deposition of inhaled aerosols, as well as for use as a reference during diagnosis of unhealthy patients. The specific procedure developed could also be applied to build standard nasal geometries for different identifiable groups within the larger population.

Hydrodynamic Response of Northeastern Gulf of Mexico to Hurricanes

The northeastern Gulf of Mexico in the USA is extremely susceptible to the impacts of tropical cyclones because of its unique geometric and topographic features. Focusing on Hurricanes Ivan (2004) and Katrina (2005), this paper has addressed four scientific questions on this area’s response to hurricanes: (1) How does the shallow, abandoned Mississippi delta contribute to the storm surge? (2) What was the controlling factor that caused the record-high storm surge of Hurricane Katrina? (3) Why are the responses of an estuary to Hurricanes Ivan and Katrina so different from the corresponding surges on the open coast? (4) How would the storm surge differ if Hurricane Katrina had taken a different course? Guided by field observations of winds, waves, water levels, and currents, two state-of-the-art numerical models for storm surges and wind waves have been coupled to hindcast the relevant hydrodynamic conditions, including storm surges, surface waves, and depth-averaged currents. Fairly good agreement between the modeled and measured surge hydrographs was found. The quantitative numerical simulations and simple qualitative analysis have revealed that the record-high storm surge of Hurricane Katrina was caused by the interaction of the surge with the extremely shallow, ancient deltaic lobe of Mississippi River. A hypothetical scenario formed by shifting the path of Hurricane Katrina to the observed path of Hurricane Frederic (1979) resulted in a much smaller surge than that observed in coastal Mississippi and Louisiana. However, this scenario did still result in a high surge near the head of Mobile Bay. One of the important lessons learned from Hurricane Katrina is that the Saffir–Simpson scale should be systematically revised to reflect the topographic and geometric features of a complex, heterogeneous coast, including the possible surge amplification in an estuary or a submerged river delta.

SU‐GG‐T‐294: A New Cone‐Beam CT Daily QA Phantom for Stereotactic Radiosurgery

Purpose: In Stereotactic Radiosurgery (SRS), sub‐milimeter accuracy for patient setup is necessary. We developed a phantom for SRS using CBCT for patient alignment. Method and Materials: The phantom is a semi‐spherical shaped acrylic with the dimension of 11 cm diameter and 12 cm height. It consists of four sections: hollow cone‐shaped top, house‐made large water level, metal target supporter with 15 mm diameter stainless steel ball target and hollow cone offset between radiation and mechanical axis of the CT canner. The bottom of the phantom is attached to a frame that can be placed on treatment table of the linear accelerator. The phantom was scanned by using diagnose CT and exported to the ADAC Pinnacle planning computer. The phantom is then aligned by using lasers and CBCT images are taken. The image correlation was carried by comparing external contours of the phantom itself and two contours of the chamber in the phantom. Results: The geometrical accuracy of the stereotactic radiosurgery system using the CBCT as secondary double check was investigated over 8 different gantry angles and table rotations, and their average uncertainty is approximately 0.5 mm in three major orientations with maximum 0.8mm errors. Four physicists were asked to do image fusion, intra‐user variations were less than 0.25mm. The dosimetric uncertainties of 75% isodose volumes were also evaluated. Between planning computer and film irradiation, the uncertainties were less than 1 mm in three major axis. Conclusion: The CT and CBCT images can be correlated with 0.5mm steps. The daily QA phantom was very effective to investigate any systematic errors including CT images, planning procedure, geometrical uncertainty of CBCT, and gantry flex of the linear accelerator. The unique geometrical features of the phantom provide minimum intra‐user variations with 0.5mm uncertainty, which is comparable to the setup uncertainty of the laser.

Functionalized aromatics aligned with the three Cartesian axes: Extension of centropolyindane chemistry

The unique geometrical features and structural potential of the centropolyindanes, a complete family of novel, 3D polycyclic aromatic hydrocarbons, are discussed with respect to the inherent orthogonality of their arene units. Thus, the largest member of the family, centrohexaindane, a topologically nonplanar hydrocarbon, is presented as a "Cartesian hexabenzene", because each of its six benzene units is stretched into one of the six directions of the Cartesian space. This feature is discussed on the basis of the X-ray crystal structures of centrohexaindane and two lower members of the centropolyindane family, viz. the parent tribenzotriquinacenes. Recent progress in multiple functionalization and extension of the indane wings of selected centropolyindanes is reported, including several highly efficient six- and eight-fold C-C cross-coupling reactions. Some particular centropolyindane derivatives are presented, such as the first twelve-fold functionalized centrohexaindane and a tribenzotriquinacene bearing three mutually orthogonal phenanthroline groupings at its molecular periphery. Challenges to further extend the arene peripheries of the tribenzotriquinacenes and fenestrindanes to give, eventually, graphite cuttings bearing a central bowl- or saddle-shaped center are outlined, as is the hypothetical generation of a "giant" nanocube consisting of eight covalently bound tribenzotriquinacene units. Along these lines, our recent discovery of a related, solid-state supramolecular cube, containing eight molecules of a particular tribromotrinitrotribenzotriquinacene of the same absolute configuration, is presented for the first time.

Raman scattering and field-emission properties of RuO2 nanorods

We report Raman scattering and field emission properties of rutile RuO2 nanorods obtained by metalorganic chemical vapor deposition. The RuO2 nanorods have lengths up to several micrometers and diameters in the range of 10–50 nm. The nanosize dependencies of the peak shift and the broadening of the three first-order Raman modes agree well with those calculated on the basis of the phonon confinement model. The unique geometrical features of RuO2 nanorods exhibit a strong effect on field enhancement (β∼1153), which results in a low threshold field (Eth∼4.9V∕μm) defined at the beginning of emission. The low turn-on field for driving a current of 10μA∕cm2 is about 10.3V∕μm, which is comparable with amorphous carbon film. Our results indicate that RuO2 nanorods provide an excellent alternative for field emitter due to several advantages, including nanometer structure, natural conductor, enhanced resistance to oxidation, and long-term stability.

Fractile arrays: a new class of tiled arrays with fractal boundaries

In this paper, a new class of antenna arrays are introduced, which we call fractile arrays. A fractile array is defined as any array with a fractal boundary contour that tiles the plane without gaps or overlaps. It will be shown that the unique geometrical features of fractiles may be exploited in order to make available a family of deterministic arrays that offer several highly desirable performance advantages over their conventional periodic planar array counterparts. Most notably, fractile arrays have no grating lobes even when the minimum spacing between elements is increased to at least one-wavelength. This has led to the development of a new design methodology for modular broadband low-sidelobe arrays that is based on fractal tilings. Several examples of fractile arrays will be considered including Peano-Gosper, terdragon, 6-terdragon, and fudgeflake arrays. Efficient iterative procedures for calculating the radiation patterns of these fractile arrays to arbitrary stage of growth P are also introduced in this paper.

Field emission from vertically aligned conductive IrO2 nanorods

We report on the preparation and field-emission properties of vertically aligned conductive IrO2 nanorods. The unique geometrical features of IrO2 nanorods, including nanosized structure and self-assembled sharp tip, exhibit a strong effect on field enhancement (β∼40 000), which result in a low threshold field (Eth∼0.7 V/μm) defined at the beginning of emission. A low turn-on field for driving a current of 10 μA/cm2 is about 5.6 V/μm, which is comparable with the carbon nanotube, diamond, and amorphous carbon. The potential of using IrO2 nanorods as an emitter material has been demonstrated.

Spectroscopic study of [Fe2O2(5-Et3-TPA)2]3+: nature of the Fe2O2 diamond core and its possible relevance to high-valent binuclear non-heme enzyme intermediates.

The spectroscopic properties and electronic structure of an Fe(2)(III,IV) bis-mu-oxo complex, [Fe(2)O(2)(5-Et(3)-TPA)(2)](ClO(4))(3) where 5-Et(3)-TPA = tris(5-ethyl-2-pyridylmethyl)amine, are explored to determine the molecular origins of the unique electronic and geometric features of the Fe(2)O(2) diamond core. Low-temperature magnetic circular dichroism (MCD) allows the two features in the broad absorption envelope (4000-30000 cm(-)(1)) to be resolved into 13 transitions. Their C/D ratios and transition polarizations from variable temperature-variable field MCD saturation behavior indicate that these divide into three types of electronic transitions; t(2) --> t(2) involving excitations between metal-based orbitals with pi Fe-O overlap (4000-10000 cm(-)(1)), t(2)/t(2) --> e involving excitations to metal-based orbitals with sigma Fe-O overlap (12500-17000 cm(-)(1)) and LMCT (17000-30000 cm(-)(1)) and allows transition assignments and calibration of density functional calculations. Resonance Raman profiles show the C(2)(h)() geometric distortion of the Fe(2)O(2) core results in different stretching force constants for adjacent Fe-O bonds (k(str)(Fe-O(long)) = 1.66 and k(str)(Fe-O(short)) = 2.72 mdyn/A) and a small ( approximately 20%) difference in bond strength between adjacent Fe-O bonds. The three singly occupied pi-metal-based orbitals form strong superexchange pathways which lead to the valence delocalization and the S = (3)/(2) ground state. These orbitals are key to the observed reactivity of this complex as they overlap with the substrate C-H bonding orbital in the best trajectory for hydrogen atom abstraction. The electronic structure implications of these results for the high-valent enzyme intermediates X and Q are discussed.

Synthesis, structure, and bonding of BaTl(3): an unusual competition between cluster and classical bonding in the thallium layers.

The new BaTl(3) compound has been synthesized and characterized by physical property measurements and electronic structure calculations. Its structure (Cmcm) is a new intermediate in the Ni(3)Sn family (P6(3)/mmc), and consists of thallium layers formed from two-center bond formation between the parallel chains of face-sharing octahedral clusters. The valence electron concentration (VEC) of the thallium layers is consistent with their two-dimensional nature, in comparison with those in other AX(3)-type compounds with one- or three-dimensional anionic networks with the same building blocks and different VECs. The unique geometric features of the anionic thallium layers bring on an unusual competition between inter- and intracluster bonds. Detailed studies of the energetics of BaTl(3) reveal for the first time the important role of cation-anion interactions in the bonding competition in such an anionic substructure.

DNA deformability as a recognition feature in the reverb response element.

Most nuclear receptors recognize the same consensus hexameric sequence, AGGTCA. An important question has been how the various members of this transcription factor family distinguish identity features in these closely related DNA sites. We determined structures from several crystal forms of the RevErb-DNA complex and analyzed the patterns of protein-DNA interactions and DNA distortions. We found a significant and consistent DNA distortion at a TA step directly preceding the first consensus 5'-AGGTCA-3' recognition sequence. Importantly, while this base-pair sequence is associated with RevErb's high-affinity sites, there are no sequence-specific contacts formed with the protein. Our study shows that RevErb relies instead on the intrinsic geometry and flexibility of this TA site to make the required fit between the proteins' independent major groove and minor groove binding interactions, which occur on both sides of the TA step. Our findings extend the description of response element discrimination to include a role for sequence-dependent DNA deformations and suggest how other monomeric members of this superfamily, such as NGFI-B, SF-1, and ROR, could also recognize unique geometric features in their DNA targets.

The clinical radiobiology of brachytherapy.

The unique geometrical features of brachytherapy, together with the wide variety of temporal patterns of dose delivery, result in important interactions between physics and radiobiology. These interactions exert a major influence on the way in which brachytherapy treatments should be evaluated, both in absolute and comparative terms. This article reviews the main physical and radiobiological aspects of brachytherapy and considers examples of their influence on specific types of treatment. The issues relating to the optimization of high dose rate brachytherapy are presented, together with the implications of multiphasic repair kinetics for low dose-rate and pulsed high dose rate brachytherapy. The opportunities for application of radiobiological principles to improve various brachytherapy techniques, together with the integration of brachytherapy with teletherapy, are also outlined. Equations for the numerical evaluation of brachytherapy treatments are presented in the Appendices.

Aerosol transport and deposition in the rhythmically expanding pulmonary acinus.

Little is known about factors controlling the dynamics of aerosol dispersion and deposition in the lung periphery, though this knowledge becomes increasingly important in many fields such as environmental and occupational exposure, diagnostic applications, and therapeutic deliver of drugs via aerosols. For the last several years, we have been studying aerosol behavior in the pulmonary acinus, where the airway structure and the associated fluid mechanics are distinctly different from those in the conducting airways. Our major research efforts have been focused on the basic physics underlying acinar fluid mechanics and particle dynamics, which are likely to be conditioned by the two key geometric factors of acinar airways: structural alveolation and rhythmic expansion and contraction of the alveolar walls. A combination of computational and experimental analyses revealed that due to these unique geometric features acinar flow can be extremely complex despite the low Reynolds number, and can have substantial effects on particle dynamics. In particular, chaotic mixing can occur in the lung periphery. In the course of such a mixing process, the inhaled aerosol particles quickly mix with the residual alveolar gas in a manner that is radically different from the previously considered classical diffusion process. The objective of this paper is to briefly review our current understanding of these processes, to discuss existing deposition models, and to describe our ongoing research efforts toward a basic understanding of aerosol behavior in the pulmonary acinus.

Transverse relaxation in supported and nonsupported phospholipid model membranes and the influence of ultraslow motions: A 31P-NMR study

The effect of motions which are slow on the NMR time scale (in particular, lateral diffusion) on the 31P-NMR transverse relaxation behavior of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) phospholipid membranes was studied by experiment and computer simulation. Two new membrane model systems (spherical supported vesicles) which exhibit some unique geometrical features and physical properties as well as the commonly used multilamellar vesicles, were applied for the measurement of the 31P-NMR anisotropic transverse relaxation times. The known geometry of the new membrane model systems under study enables a direct comparison of the experimental transverse relaxation spectra with those obtained by a spectral simulation technique which considers random diffusion on the surface of a sphere as the dominant relaxation mechanism, where the sphere size corresponds to that used in the experiments. The transverse relaxation times obtained experimentally for the three model systems studied differ drastically, where the multilamellar vesicles exhibit the longest T2 and single spherical supported bilayers show the shortest relaxation time. Both experiment and simulation indicate that lateral diffusion causes an anisotropic transverse relaxation which scales with the angle θ between molecular director axis and magnetic field as 1/T2∼sin2θ cos2θ. An analysis of the experimental data obtained for supported systems suggests that diffusion of the individual molecules along the surface of the sphere is superimposed by diffusion over an ‘‘adiabatic rough’’ surface (a ‘‘quasistationary ’’ roughness on the time scale of the echo experiment). This provides a significant additional contribution to the transverse relaxation time T2. A comparison of single bilayers and multibilayers on a solid support, respectively, indicates that this roughness is mainly a property of the single supported bilayers, most likely due to an area mismatch between the bilayer and the surface of its solid support.

キラルアレン合成素子を活用した分子骨格の構築

Allenes comprize that class of compounds characterized by a 1, 2-diene grouping with an unique geometrical feature owing to the cumulated diene system. Within the last ten years, allene chemistry has considerable progressed to development of modern synthetic methodologies for a variety of desirable intermediate and natural products. On the other hand, allenes also enjoy a wide variety of reactivities in many types of reactions via ionic, radical or concerted mechanism.Here we describe the review of recent studies on syntheses of chiral allenes and cyclic compounds including heterocyclic compounds as lactones, furans, indoles, pyrrolidines, thiophenes, sulfolenes, macrolides, oxazolidinones using allenes as versatile building blocks (synthons).

Some important geometrical features of conic-section-generated offset refelector antennas

Geometrical characteristics of conic-section-generated offset reflectors are studied in a unified fashion. Some unique geometrical features of the reflector rim constructed from the intersection of the reflector surface and a cone or cylinder are explored in detail. It is found that the intersection curve (rim) of the rotationally generated conic-section reflector surface and a circular cone with its tip at the focal point is always a planar curve and has a circular projection on the focal plane only for the offset parabolic reflector. Furthermore, in this case, the line going through the center of the circle, parallel to the focal axis, and the central axis of the cone do not intersect the reflector surface at the same point. Numerical results are presented to demonstrate some unique features of offset parabolic reflectors.

Factorability of the Hessian of the binding polynomial. The central issues concerning statistical ratios between binding constants, hill plot slope and positive and negative co-operativity

1. (1) It is demonstrated that arguments as to co-operativity based upon the sign of co-operativity coefficients, factorability of the binding polynomial, sigmoid binding isotherms, concavity of double reciprocal plots or other graphical features are ambiguous. 2. (2) The sole unambiguous test for positive or negative co-operativity in the base of ligand binding to a macromolecule is the magnitude of the Hill plot slope with respect to unity as a function of ligand concentration. 3. (3) This is entirely dependent on the factorability of the Hessian of the binding polynomial where there is no aggregation of the macromolecule and in any graphical space changes in co-operativity occur at positive roots of the Hessian. Each graphical space will then have a unique geometric feature associated with these roots and this will constitute the test for positive or negative co-operativity in that space. 4. (4) The algebraic properties of the Hessian are described and the relationship between the roots of a polynomial and its concomitants are given and related to roots of the Hessian for the binary cubic and quartic. 5. (5) This study leads to the conclusion that co-operativity has not yet been satisfactorily defined for steady-state systems but for homotropic effects resulting from ligand binding to a single protein species the sign of co-operativity is the same as the sign of the Hessian of the allosteric binding polynomial. Although this can be determined experimentally, it is proved that, in the fourth degree case, it is not always then possible to infer the sign of the co-operativity coefficients or nature of the factorability of the binding polynomial since, unlike the second and third degree cases, the fourth degree Hill plot shapes are ambiguous. 6. (6) When the macromolecule aggregates in addition to binding ligand there is no binding polynomial and no Hessian but in these circumstances there is always a corresponding function, the tact invariant, the sign of which is the same as the sign of the homotropic co-operativity. The reason that the Hessian is of importance when there is a binding polynomial is because in this case the Hessian functions as the tact-invariant of the actual binding isotherm and the reference curve corresponding to ligand binding to a single site at the corresponding degree of saturation.