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Articles 781 - 810 of 832

Full-Text Articles in Astrophysics and Astronomy

Setting Upper Limits On The Strength Of Periodic Gravitational Waves From Psr J1939+2134 Using The First Science Data From The Geo 600 And Ligo Detectors, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres Jan 2004

Setting Upper Limits On The Strength Of Periodic Gravitational Waves From Psr J1939+2134 Using The First Science Data From The Geo 600 And Ligo Detectors, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres

Physics & Astronomy Faculty Publications

Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar’s gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar’s equatorial ellipticity.


Analysis Of Ligo Data For Gravitational Waves From Binary Neutron Stars, B. P. Abbott, R. Abbott, Wm. R. Johnston, Joseph D. Romano, V. Schmidt Jan 2004

Analysis Of Ligo Data For Gravitational Waves From Binary Neutron Stars, B. P. Abbott, R. Abbott, Wm. R. Johnston, Joseph D. Romano, V. Schmidt

Physics & Astronomy Faculty Publications

We report on a search for gravitational waves from coalescing compact binary systems in the Milky Way and the Magellanic Clouds. The analysis uses data taken by two of the three LIGO interferometers during the first LIGO science run and illustrates a method of setting upper limits on inspiral event rates using interferometer data. The analysis pipeline is described with particular attention to data selection and coincidence between the two interferometers. We establish an observational upper limit of R


Analysis Of First Ligo Science Data For Stochastic Gravitational Waves, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano Jan 2004

Analysis Of First Ligo Science Data For Stochastic Gravitational Waves, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano

Physics & Astronomy Faculty Publications

We present the analysis of between 50 and 100 h of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a f−3 power spectrum of …


Using The Intensity Modulation Index To Test Pulsar Radio Emission Models, Fredrick A. Jenet, Janusz Gil Oct 2003

Using The Intensity Modulation Index To Test Pulsar Radio Emission Models, Fredrick A. Jenet, Janusz Gil

Physics & Astronomy Faculty Publications

This Letter explores the possibility of testing pulsar radio emission models by observing pulse-to-pulse intensity modulation. It is shown that a relationship between a pulsar's period, period derivative, and intensity modulation is a natural consequence of at least one theoretical model of radio pulsar emission. It is proposed that other models may also predict a similar correlation. The exact form of the relationship will depend on the model in question. Hence, observations of intensity modulation should be able to determine the validity of the various emission models. In an attempt to search for the predicted dependencies, the modulation properties of …


Gravitational Radiation From Pulsating White Dwarfs, Matthew Benacquista, M. Benacquista, D. M. Sedrakian, M. V. Hairapetyan, K. M. Shahabasyan, A. A. Sadoyan Oct 2003

Gravitational Radiation From Pulsating White Dwarfs, Matthew Benacquista, M. Benacquista, D. M. Sedrakian, M. V. Hairapetyan, K. M. Shahabasyan, A. A. Sadoyan

Physics & Astronomy Faculty Publications

Rotating white dwarfs undergoing quasi-radial oscillations can emit gravitational radiation in a frequency range from 0.1 to 0.3 Hz. Assuming that the energy source for the gravitational radiation comes from the oblateness of the white dwarf induced by the rotation, the strain amplitude is found to be ∼10-27 for a white dwarf at ∼50 pc. The Galactic population of these sources is estimated to be ∼107 and may produce a confusion-limited foreground for proposed advanced detectors in the frequency band between space-based and ground-based interferometers. Nearby oscillating white dwarfs may provide a clear enough signal to investigate white dwarf interiors …


Normal And Lateral Casimir Forces Between Deformed Plates, Thorsten Emig, Andreas Hanke, Ramin Golestanian, Mehran Kardar Feb 2003

Normal And Lateral Casimir Forces Between Deformed Plates, Thorsten Emig, Andreas Hanke, Ramin Golestanian, Mehran Kardar

Physics & Astronomy Faculty Publications

The general path-integral formulation was set up for Casimir energy of the electromagnetic gauge field. By separating into transversal electric and magnetic modes, the problem was reduced to two decoupled problems for scalar fields which differ only in their boundary conditions. In each case, the Casimir energy was calculated for general plate deformations perturbatively. Results on both the normal and the lateral force between sinusoidally corrugated plates were outlined.


Spontaneous Magnetization Generated By Spin, Pulsating, And Planar Combustion Synthesis, Karen S. Martirosyan, J. R. Claycomb, G. Gogoshin, R. A. Yarbrough, J. H. Miller Jr., D. Luss Jan 2003

Spontaneous Magnetization Generated By Spin, Pulsating, And Planar Combustion Synthesis, Karen S. Martirosyan, J. R. Claycomb, G. Gogoshin, R. A. Yarbrough, J. H. Miller Jr., D. Luss

Physics & Astronomy Faculty Publications

The motion of the high temperature front during combustion synthesis of ferrite materials generates residual magnetization in cylindrical product samples. The combustion wave created a current density of up to 10 A/cm2, which influenced the magnetization distribution. The measured peak magnetic field intensity was up to 8 mT. Qualitatively different magnetic field maps were generated in ferrite samples synthesized by different combustion modes. The average magnetization vector generated by either planar or pulsating combustion was oriented at a smaller angle with respect to the pellet axis ~f<45°! than those generated by spin combustion ~60°


Mode-Cleaning And Injection Optics Of The Gravitational-Wave Detector Geo600, S. Goßler, M. M. Casey, A. Grant, H. Grote, Volker Quetschke Jan 2003

Mode-Cleaning And Injection Optics Of The Gravitational-Wave Detector Geo600, S. Goßler, M. M. Casey, A. Grant, H. Grote, Volker Quetschke

Physics & Astronomy Faculty Publications

The British–German interferometric gravitational-wave detector GEO600 uses two high-finesse triangular ring cavities of 8 m optical pathlength each, as an optical mode-cleaning system. The modecleaner system is housed in an ultrahigh-vacuum environment to avoid contamination of the optics and to minimize both the influence of refractive index variations of the air and acoustic coupling to the optics. To isolate the cavities from seismic noise, all optical components are suspended as double pendulums. These pendulums are damped at their resonance frequencies at the upper pendulum stage with magnet-coil actuators. A suspended reaction mass supports three coils matching magnets bonded onto the …


Comment On ‘‘Why Is The Dna Denaturation Transition First Order?’’, Andreas Hanke, Ralf Metzler Jan 2003

Comment On ‘‘Why Is The Dna Denaturation Transition First Order?’’, Andreas Hanke, Ralf Metzler

Physics & Astronomy Faculty Publications

A Comment on the Letter by . The authors of the Letter offer a Reply.


Horizontal-Branch Morphology And The Photometric Evolution Of Old Stellar Populations, Hyun Chul Lee, Young Wook Lee, Brad K. Gibson Nov 2002

Horizontal-Branch Morphology And The Photometric Evolution Of Old Stellar Populations, Hyun Chul Lee, Young Wook Lee, Brad K. Gibson

Physics & Astronomy Faculty Publications

Theoretical integrated broadband colors ranging from far-UV to near-IR have been computed for old stellar systems from our evolutionary population synthesis code. These models take into account, for the first time, the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. Our models show that some temperature-sensitive color indices are significantly affected by the presence of blue HB stars. In particular, B-V does not become monotonically redder as metallicity increases at given ages, but becomes bluer by as much as ∼0.15 mag because of the contribution from blue HB stars. Similar trends are also found in the Washington …


Equilibrium Shapes Of Flat Knots, Ralf Metzler, Andreas Hanke, Paul G. Dommersnes, Yacov Kantor, Mehran Kardar May 2002

Equilibrium Shapes Of Flat Knots, Ralf Metzler, Andreas Hanke, Paul G. Dommersnes, Yacov Kantor, Mehran Kardar

Physics & Astronomy Faculty Publications

The equilibrium shapes of prime and composite knots were studied. It was showed that the topological details of prime knots were localized on a small portion of the larger ring polymer due to self-avoiding effects. The original knot configuration could assume a hierarchy of contracted shape, the dominating one given by one small loop, within this region. For the flat trefoil knot, this hierarchy was studied in detail and corroborated by Monte Carlo simulations.


Group-Fitted Ab Initio Single- And Multiple-Scattering Exafs Debye-Waller Factors, Nicholas Dimakis, Grant Bunker Jan 2002

Group-Fitted Ab Initio Single- And Multiple-Scattering Exafs Debye-Waller Factors, Nicholas Dimakis, Grant Bunker

Physics & Astronomy Faculty Publications

X-ray absorption fine structure (XAFS) spectroscopy is one of the few direct probes of the structure of metalloprotein binding that is equally applicable to proteins in crystals, solutions, and membranes. Despite considerable progress in the calculation of the photoelectron scattering aspects of XAFS, calculation of the vibrational aspects has lagged because of the difficulty of the calculations. We report here initial results that express single- and multiple-scattering Debye-Waller factors as polynomial functions of first shell radial distance for metal-peptide complexes, enabling quantitatively accurate full multiple-scattering XAFS data analysis of active sites of unknown structure at arbitrary temperatures without the use …


Tightness Of Slip-Linked Polymer Chains, Ralf Metzler, Andreas Hanke, Paul G. Dommersnes, Yacov Kantor, Mehran Kardar Jan 2002

Tightness Of Slip-Linked Polymer Chains, Ralf Metzler, Andreas Hanke, Paul G. Dommersnes, Yacov Kantor, Mehran Kardar

Physics & Astronomy Faculty Publications

We study the interplay between entropy and topological constraints for a polymer chain in which sliding rings (slip links) enforce pair contacts between monomers. These slip links divide a closed ring polymer into a number of subloops which can exchange length among each other. In the ideal chain limit, we find the joint probability density function for the sizes of segments within such a slip-linked polymer chain (paraknot). A particular segment is tight (small in size) or loose (of the order of the overall size of the paraknot) depending on both the number of slip links it incorporates and its …


Correlation Functions Near Modulated And Rough Surfaces, Andreas Hanke, Mehran Kardar Jan 2002

Correlation Functions Near Modulated And Rough Surfaces, Andreas Hanke, Mehran Kardar

Physics & Astronomy Faculty Publications

In a system with long-ranged correlations, the behavior of correlation functions is sensitive to the presence of a boundary. We show that surface deformations strongly modify this behavior as compared to a flat surface. The modified near surface correlations can be measured by scattering probes. To determine these correlations, we develop a perturbative calculation in the deformations in height from a flat surface. Detailed results are given for a regularly patterned surface, as well as for a self-affinely rough surface with roughness exponent ζ. By combining this perturbative calculation in height deformations with the field-theoretic renormalization-group approach, we also estimate …


The First Detection Of Coherent Emission From Radio Pulsars, F. A. Jenet, S. B. Anderson, T. A. Prince Sep 2001

The First Detection Of Coherent Emission From Radio Pulsars, F. A. Jenet, S. B. Anderson, T. A. Prince

Physics & Astronomy Faculty Publications

The statistical properties of the radio emission from the pulsars B0823+26, B0950+08, B1133+16, and B1937+21 are studied using high time resolution observations taken at the Arecibo Observatory in Puerto Rico. Temporally coherent non-Gaussian emission has been detected in three of the four observed objects. This is the first time such a phenomenon has been observed. The results have been interpreted using a generalized shot noise model, and various basic physical quantities pertaining to the magnetospheric plasma have been estimated.


Data Conditioning For Gravitational Wave Detectors: A Kalman Filter For Regressing Suspension Violin Modes, L. S. Finn, S. Mukherjee Aug 2001

Data Conditioning For Gravitational Wave Detectors: A Kalman Filter For Regressing Suspension Violin Modes, L. S. Finn, S. Mukherjee

Physics & Astronomy Faculty Publications

Interferometric gravitational wave detectors operate by sensing the differential light travel time between free test masses. Correspondingly, they are sensitive to anything that changes the physical distance between the test masses, including physical motion of the masses themselves. In ground-based detectors the test masses are suspended as pendula, in order that they be approximately \"free\" above the pendulumn frequency. Still, thermal or other excitations of the suspension wires' violin modes do impart a force on the masses that appears as a strong, albeit narrow-band, \"signal\" in the detectors waveband. Gravitational waves, on the other hand, change the distance between the …


Verification Of A Distortion In The Microstructure Of Gan Detected By Exafs Using Ab Initio Density Functional Theory Calculations, Nicholas Dimakis, Grant Bunker, M. Katsikini, E. C. Paloura Jan 2001

Verification Of A Distortion In The Microstructure Of Gan Detected By Exafs Using Ab Initio Density Functional Theory Calculations, Nicholas Dimakis, Grant Bunker, M. Katsikini, E. C. Paloura

Physics & Astronomy Faculty Publications

X-ray absorption fine structure (XAFS) measurements on a series of epitaxially grown GaN samples have shown a distortion in the microstructure of GaN. More specifically the central N atom is 4-fold coordinated but the four Ga atoms are not equidistant. It has been shown that 2.9 to 3.5 of them (depending on the growth conditions) are found in the expected from XRD distance of 1.94 A and the remaining are at a distance longer by approximately 15%. Second derivative calculation of the conformation energy using the Density Functional Theory (DFT) is used to investigate if the symmetric GaN cluster as …


Chemical Transferability Of Single- And Multiple-Scattering Exafs Debye-Waller Factors, Nicholas Dimakis, Grant Bunker Jan 2001

Chemical Transferability Of Single- And Multiple-Scattering Exafs Debye-Waller Factors, Nicholas Dimakis, Grant Bunker

Physics & Astronomy Faculty Publications

Single- and multiple-scattering EXAFS Debye-Waller factors are amplitude reduction parameters that appear in the EXAFS x(k) equation accounting for the structural and thermal disorder of a given sample. These parameters must be known accurately in order to obtain quantitative agreement between theory and experiment. Since experimental data can only support a limited number of fitted parameters these factors must be known from another source. Although various approaches have been considered in the past with a variety of results, the self-consistent ab initio Density functional theory stands for the most accurate and reliable method regardless of molecular symmetry or other specific …


Apex Version 2.0: Latest Version Of The Cross-Platform Analysis Program For Exafs, Nicholas Dimakis, Grant Bunker Jan 2001

Apex Version 2.0: Latest Version Of The Cross-Platform Analysis Program For Exafs, Nicholas Dimakis, Grant Bunker

Physics & Astronomy Faculty Publications

This report describes recent progress on APEX, a free, open source, cross platform set of EXAFS data analysis software. In a previous report we described APEX 1.0 (Dimakis, N. and Bunker, G., 1999), a free and open source code suite of basic X-Ray Absorption Fine Structure (XAFS) data analysis programs for classical data reduction and single scattering analysis. The first version of APEX was the only cross platform (linux/irix/windows/MacOS) EXAFS analysis program to our knowledge, but it lacked important features like multiple scattering fitting, generic format conversion from ASCII to University of Washington (UW) binary-type files, and user friendly interactive …


Probing The Strong Boundary Shape Dependence Of The Casimir Force, Thorsten Emig, Andreas Hanke, Ramin Golestanian, Mehran Kardar Jan 2001

Probing The Strong Boundary Shape Dependence Of The Casimir Force, Thorsten Emig, Andreas Hanke, Ramin Golestanian, Mehran Kardar

Physics & Astronomy Faculty Publications

We study the geometry dependence of the Casimir energy for deformed metal plates by a path integral quantization of the electromagnetic field. For the first time, we give a complete analytical result for the deformation induced change in Casimir energy δE in an experimentally testable, nontrivial geometry, consisting of a flat and a corrugated plate. Our results show an interesting crossover for δE as a function of the ratio of the mean plate distance H, to the corrugation length λ: For λ≪H we find a slower decay ∼H−4, compared to the H−5 behavior predicted by the commonly used pairwise summation …


Single-Pulse Characteristics Of The Millisecond Radio Pulsar Psr B1937 + 21 At 430 Mhz, F. A. Jenet, S. B. Anderson, T. A. Prince Jan 2001

Single-Pulse Characteristics Of The Millisecond Radio Pulsar Psr B1937 + 21 At 430 Mhz, F. A. Jenet, S. B. Anderson, T. A. Prince

Physics & Astronomy Faculty Publications

The single-pulse characteristics of the millisecond pulsar PSR B1937 + 21 are studied using the recently installed Caltech baseband recorder at the Arecibo Radio Observatory in Puerto Rico. This is the first such analysis of this object that includes both average intensity pulses as well as \"giant pulses.\" Pulse ensemble-averaging techniques are developed in order to study the characteristics of PSR B1937 + 21's single pulses since the high time resolution signal-to-noise ratio is less than unity. This analysis reveals that the non-giant pulse radio emission is extremely stable. All observed fluctuations are consistent with diffractive interstellar scattering. Such intrinsic …


Polymer Depletion Interaction Between Two Parallel Repulsive Walls, F. Schlesener, Andreas Hanke, R. Kimpel, S. Dietrich Jan 2001

Polymer Depletion Interaction Between Two Parallel Repulsive Walls, F. Schlesener, Andreas Hanke, R. Kimpel, S. Dietrich

Physics & Astronomy Faculty Publications

The depletion interaction between two parallel repulsive walls confining a dilute solution of long and flexible polymer chains is studied by field-theoretic methods. Special attention is paid to self-avoidance between chain monomers relevant for polymers in a good solvent. Our direct approach avoids the mapping of the actual polymer chains on effective hard or soft spheres. We compare our results with recent Monte Carlo simulations [A. Milchev and K. Binder, Eur. Phys. J. B 3, 477 (1998)] and with experimental results for the depletion interaction between a spherical colloidal particle and a planar wall in a dilute solution of nonionic …


Modified Critical Correlations Close To Modulated And Rough Surfaces, Andreas Hanke, Mehran Kardar Jan 2001

Modified Critical Correlations Close To Modulated And Rough Surfaces, Andreas Hanke, Mehran Kardar

Physics & Astronomy Faculty Publications

Correlation functions are sensitive to the presence of a boundary. Surface modulations give rise to modified near surface correlations, which can be measured by scattering probes. To determine these correlations, we develop a perturbative calculation in deformations in height from a flat surface. The results, combined with a renormalization group around four dimensions, are also used to predict critical behavior near a self-affine rough surface. We find that a large enough roughness exponent can modify surface critical behavior.


Detection Of Variable Frequency Signals Using A Fast Chirp Transform, F. A. Jenet, T. A. Prince Dec 2000

Detection Of Variable Frequency Signals Using A Fast Chirp Transform, F. A. Jenet, T. A. Prince

Physics & Astronomy Faculty Publications

The detection of signals with varying frequency is important in many areas of physics and astrophysics. The current work was motivated by a desire to detect gravitational waves from the binary inspirai of neutron stars and black holes, a topic of significant interest for the new generation of interferometric gravitational wave detectors such as LIGO. However, this work has significant generality beyond gravitational wave signal detection. We define a fast chirp transform (FCT) analogous to the fast Fourier transform. Use of the FCT provides a simple and powerful formalism for detection of signals with variable frequency just as Fourier transform …


P-Selectin Or Intercellular Adhesion Molecule (Icam)-1 Deficiency Substantially Protects Against Atherosclerosis In Apolipoprotein E-Deficient Mice, Robert G. Collins, Rizwan Velji, Natalia V. Guevara, M. John Hicks, Lawrence Chan, Arthur L. Beaudet Jan 2000

P-Selectin Or Intercellular Adhesion Molecule (Icam)-1 Deficiency Substantially Protects Against Atherosclerosis In Apolipoprotein E-Deficient Mice, Robert G. Collins, Rizwan Velji, Natalia V. Guevara, M. John Hicks, Lawrence Chan, Arthur L. Beaudet

Physics & Astronomy Faculty Publications

The expression of leukocyte and endothelial cell adhesion molecules (CAMs) is essential for the emigration of leukocytes during an inflammatory response. The importance of the inflammatory response in the development of atherosclerosis is indicated by the increased expression of adhesion molecules, proinflammatory cytokines, and growth factors in lesions and lesion-prone areas and by protection in mice deficient in various aspects of the inflammatory response. We have quantitated the effect of deficiency for intercellular adhesion molecule (ICAM)-1, P-selectin, or E-selectin on atherosclerotic lesion formation at 20 wk of age in apolipoprotein (apo) E(- /-) (deficient) mice fed a normal chow diet. …


Robust Test For Detecting Nonstationarity In Data From Gravitational Wave Detectors, Soumya Mohanty Jan 2000

Robust Test For Detecting Nonstationarity In Data From Gravitational Wave Detectors, Soumya Mohanty

Physics & Astronomy Faculty Publications

It is difficult to choose detection thresholds for tests of nonstationarity that assume a priori a noise model if the data are statistically uncharacterized to begin with. This is a potentially serious problem when an automated analysis is required, as would be the case for the huge data sets that large interferometric gravitational wave detectors will produce. A solution is proposed in the form of a robust time-frequency test for detecting nonstationarity whose threshold for a specified false alarm rate is almost independent of the statistical nature of the ambient stationary noise. The efficiency of this test in detecting bursts …


The Hî² Index As An Age Indicator Of Old Stellar Systems: The Effects Of Horizontal-Branch Stars, Hyun Chul Lee, Suk Jin Yoon, Young Wook Lee Jan 2000

The Hî² Index As An Age Indicator Of Old Stellar Systems: The Effects Of Horizontal-Branch Stars, Hyun Chul Lee, Suk Jin Yoon, Young Wook Lee

Physics & Astronomy Faculty Publications

The strength of the Hβ index is computed for the integrated spectra of model globular clusters from the evolutionary population synthesis. For the first time, these models take into account the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. Our models show that the Hβ index is significantly affected by the presence of blue HB stars. Because of the contribution from blue HB stars, the Hβ does not monotonically decrease as metallicity increases at a given age. Instead, it reaches a maximum strength when the distribution of HB stars is centered around 9500 K, the temperature at …


Critical Adsorption On Defects In Ising Magnets And Binary Alloys, Andreas Hanke Jan 2000

Critical Adsorption On Defects In Ising Magnets And Binary Alloys, Andreas Hanke

Physics & Astronomy Faculty Publications

Long-range correlations in a magnet close to its critical point or in a binary alloy close to a continuous order-disorder transition can substantially enhance the effect of local perturbations. It is demonstrated using a position-space renormalization procedure that quasi-one-dimensional defects which break the symmetry of the order parameter have pronounced effects: They cause long-range critical adsorption profiles and give rise to new universal critical exponents, which are identified and calculated using field-theoretical methods.


Gravitational Radiation From Globular Clusters, M. Benacquista Jul 1999

Gravitational Radiation From Globular Clusters, M. Benacquista

Physics & Astronomy Faculty Publications

Space-based gravitational wave detectors will have the ability to observe continuous low-frequency gravitational radiation from binary star systems. They can determine the direction to continuous sources with an angular resolution approaching tens of arcminutes. This resolution should be sufficient to identify binary sources as members of some nearby globular clusters. Thus, gravitational radiation can be used to determine the population of hard binaries in globular clusters. For particularly hard binaries, the orbital period may change as a result of gravitational wave emission. If one of these binaries can be identified with a globular cluster, then the distance to that cluster …


Critical Adsorption On Curved Objects, Andreas Hanke, S. Dietrich Jan 1999

Critical Adsorption On Curved Objects, Andreas Hanke, S. Dietrich

Physics & Astronomy Faculty Publications

A systematic field-theoretical description of critical adsorption on curved objects such as spherical or rodlike colloidal particles immersed in a fluid near criticality is presented. The temperature dependence of the corresponding order parameter profiles and of the excess adsorption are calculated explicitly. Critical adsorption on elongated rods is substantially more pronounced than on spherical particles. It turns out that, within the context of critical phenomena in confined geometries, critical adsorption on a microscopically thin ‘‘needle’’ represents a distinct universality class of its own. Under favorable conditions the results are relevant for the flocculation of colloidal particles.