Single Swift Research Articles

Swift-XRT follow-up analysis of unidentified hard X-ray sources. Searching for soft X-ray counterparts of unidentified hard X-ray sources

It has been established that the sources contributing to the cosmic X-ray background (CXB) emission are mainly nearby active galactic nuclei (AGNs), in particular those that are obscured. Thus, it is important to fully identify the hard X-ray sky source population to accurately characterize the individual contribution of different AGNs to the overall CXB emission. We present a follow-up analysis of all 218 sources marked as unidentified in our previous revision of the third release of the Palermo Swift -BAT hard X-ray catalog (3PBC) based on our multifrequency classification scheme. These 218 sources were classified as unidentified in our previous analyses because they lacked an assigned low-energy counterpart. We searched for soft X-ray counterparts of these 218 3PBC sources in archival Swift -XRT observations obtained between January 1, 2005, and August 1, 2018. In particular, we found 1213 archival Swift -XRT observations for 192 of the 218 unidentified sources. We find 93 possible Swift -XRT counterparts within the Swift -BAT positional uncertainty regions. They correspond to 73 3PBC sources, 60 of which have only a single Swift -XRT detection; the rest have multiple detections. We present all the detected possible counterparts of the as-of-yet-unidentified hard X-ray sources to the community as a catalog for future spectroscopic follow-up targets, together with a short catalog of our classification of the ten sources for which there were available spectra.

Angular momentum transfer from swift electrons to non-spherical nanoparticles within the dipolar approximation

In this work, we study the angular momentum transfer from a single swift electron to non-spherical metallic nanoparticles, specifically investigating spheroidal and polyhedral (Platonic Solids) shapes. While previous research has predominantly focused on spherical nanoparticles, our work expands the knowledge by exploring various geometries. Employing classical electrodynamics and the small particle limit, we calculate the angular momentum transfer by integrating the spectral density, ensuring causality through Fourier-transform analysis. Our findings demonstrate that prolate spheroidal nanoparticles exhibit a single blueshifted plasmonic resonance, compared to spherical nanoparticles of equivalent volume, resulting in lower angular momentum transfer. Conversely, oblate nanoparticles display two resonances — one blueshifted and one redshifted — resulting in a higher angular momentum transfer than their spherical counterparts. Additionally, Platonic Solids with fewer faces exhibit significant redshifts in plasmonic resonances, leading to higher angular momentum transfer due to edge effects. We also observe resonances and angular momentum transfers with similar characteristics in specific pairs of Platonic Solids, known as duals. These results highlight promising applications, particularly in electron tweezers technology.

Highly Sensitive Acetylcholine Biosensing Via Chemical Amplification of Enzymatic Processes in Single Track-Etched Nanochannels

Neurotransmitters are endogenous chemical messengers that play crucial roles in the transmission, enhancement and conversion of specific signals between neurons and other cells and are considered biomarkers of neurodegenerative diseases.[1] Neurodegenerative diseases cause progressive loss of cognitive and/or motor function and, as life expectancy rises, they imply major challenges for societies with rapidly aging populations.[2] As a result, monitoring neurotransmitters is becoming increasingly relevant in clinical environments. Acetylcholine (Ach) is a neurotransmitter that plays a key role in the communication between neurons in the spinal cord and nerve skeletal junctions in vertebrates. [3] Since an abnormal concentration of Ach has proven to be related to neurodegenerative diseases, novel strategies for highly sensitive and specific Ach (bio)sensing are in great demand.In this work we present the construction of Ach enzymatic biosensors with remarkable sensitivity by acetylcholinesterase immobilization on polyamine-modified single nanochannels via electrostatic self-assembly. [4] To fabricate bullet-shaped single nanochannels in polyethylene terephthalate (PET), 12 µm thick PET foils are irradiated with a single swift heavy ion. The resulting ion track consists of highly localized damaged material along the ion trajectory and is selectively dissolved in a highly basic aqueous solution under asymmetric conditions to obtain a bullet-shaped channel. The controlled PET hydrolysis exposes carboxylic groups at the channel surface (negative charge at pH < 4), which allows the immobilization of further functional groups to design and construct the biosensor.Here, we will discuss in detail the sensor design, the applied functionalization strategy, and the performance of the sensor. In short, changes in the surface charge of the nanochannel lead to measurable changes in the transmembrane current in a steady-state configuration. We will show experimental results that evidence that the designed sensor successfully transduces the presence of acetylcholine into measurable ionic signals with a 16 nM low limit of detection.[1] World Health Organization, Neurological Disorders: Public Health Challenges, World Health Organization Press, Geneva, Switzerland,2007.[2] L. Gan, M. R. Cookson, L. Petrucelli and A. R. La Spada,Nat. Neurosci., 2018, 21, 1300–1309.[3] M. Hasanzadeh, N. Shadjou and M. de la Guardia, TrAC, Trends Anal. Chem., 2017, 86, 107–121.[4] Yamili Toum Terrones, Gregorio Laucirica, Vanina M. Cayón, Gonzalo E. Fenoy, M. Lorena Cortez, María Eugenia Toimil-Molares, Christina Trautmann, Waldemar A. Mamisollé and Omar Azzaroni, Chem. Commun., 2022, 58, 10166

Direct Fabrication of Sub-10 nm Nanopores in WO3 Nanosheets Using Single Swift Heavy Ions.

Extending the fabrication methodology of solid-state nanopores in a wide range of materials is significant in the fields of single molecule detection, nanofluidic devices, and nanofiltration membranes. Here, we demonstrate a new method to directly fabricate size- and density-controllable sub-10 nm nanopores in WO3 nanosheets using single swift heavy ions (SHIs) without any chemical etching process. By selecting ions of different electronic energy losses (Se), nanopores with sizes from 1.8 to 7.4 nm can be created in WO3 nanosheets. The creation efficiency of nanopores achieves ∼100% for Se > 20 keV/nm, and there exists a critical thickness below which nanopores can be created. Combined with molecular dynamics simulations, we propose that the viscosity and surface tension of the transient molten phase caused by SHIs are the key factors for the formation of nanopores. This method paves a way to fabricate solid-state nanopores in materials with a low viscosity and surface tension.

Time-resolved high energy ionoluminescence of Al2O3

We have compared the luminescence decay from intact and pre-damaged Al2O3 crystals registered during single swift heavy ion and photo- picosecond laser pulse excitation (λex. = 440 nm). The decay curves measured during 1.2 ÷ 1.6 MeV/amu C, Ar, V, Kr, Xe ion irradiation at room temperature are composed of three components – fast (τ1 < 1 ns), τ2 = 1.8 ns (F+-centers) and τ3 = 54–80 ns (E-luminescence, the nature of emission is under discussion). The measurements performed on pre-irradiated samples have demonstrated that accumulated radiation damage suppresses the E-luminescence and only τ1 and τ2 components are observed.It was found that photoexcitation at 440 nm induces strong emission of F22+- centers with a lifetime of about 8 ns which is not detected during high energy ion irradiation. This is ascribed to the quenching effect of high density excitations in a particle track.

Direct formation of nitrogen-vacancy centers in nitrogen doped diamond along the trajectories of swift heavy ions

We report depth-resolved photoluminescence measurements of nitrogen-vacancy (NV−) centers formed along the tracks of swift heavy ions (SHIs) in type Ib synthetic single crystal diamonds that had been doped with 100 ppm nitrogen during crystal growth. Analysis of the spectra shows that NV− centers are formed preferentially within regions where electronic stopping processes dominate and not at the end of the ion range where elastic collisions lead to the formation of vacancies and defects. Thermal annealing further increases NV yields after irradiation with SHIs preferentially in regions with high vacancy densities. NV centers formed along the tracks of single swift heavy ions can be isolated with lift-out techniques for explorations of color center qubits in quasi-1D registers with an average qubit spacing of a few nanometers and of order 100 color centers per micrometer along 10 to 30-μm-long percolation chains.

Graphitization of amorphous carbon by swift heavy ion impacts: Molecular dynamics simulation

Stable C-C bonds existing in several sp hybridizations place carbon thin films of different structural compositions among the materials most tolerant to radiation damage, for applications in extreme environments. One of such applications, solid state electron stripper foils for heavy-ion accelerators, requires the understanding of the structural changes induced by high-energy ion irradiation. Tolerance of carbon structure to radiation damage, thermal effects and stress waves due to swift heavy ion impacts defines the lifetime and operational efficiency of the foils. In this work, we analyze the consequences of a single swift heavy ion impact on two different amorphous carbon structures by means of molecular dynamic simulations. The structures are constructed by using two different recipes to exclude the correlation of the evolution of sp2-to-sp3 hybridization with the initial condition. Both initial structures contain approximately 60% of sp2-bonded carbon atoms, however, with different degree of clustering of atoms with sp3 hybridization. We simulate the swift heavy ion impact employing an instantaneous inelastic thermal spike model. The analysis of changes in density, bonding content and the number and size of carbon primitive rings reveals graphitization of the material within the ion track, with higher degree of disorder in the core and more order in the outer shell. Simulated track dimensions are comparable to those observed in small angle x-ray scattering measurements of evaporation-deposited amorphous carbon stripper foils irradiated by 1.14 GeV U ions.

Transient current induced in thin film diamonds by swift heavy ions

Single crystal diamond is a suitable material for the next generation particle detectors because of the superior electrical properties and the high radiation tolerance. In order to investigate charge transport properties of diamond particle detectors, transient currents generated in diamonds by single swift heavy ions (26MeV O5+ and 45MeV Si7+) are investigated. Two dimensional maps of transient currents by single ion hits are also measured. In the case of 50μm-thick diamond, both the signal height and the collected charge are reduced by the subsequent ion hits and the charge collection time is extended. These results are thought to be attributable to the polarization effect in diamond and it appears only when the transient current is dominated by hole current. In the case of 6μm-thick diamond membrane, an “island” structure is found in the 2D map of transient currents. Signals in the islands shows different applied bias dependence from signals in other regions, indicating different crystal and/or metal contact quality. Simulation study of transient currents based on the Shockley-Ramo theorem clarifies that accumulation of space charges changes distribution of electric field in diamond and causes the polarization effect.

Observation of complete pressure-jump protein refolding in molecular dynamics simulation and experiment.

Density is an easily adjusted variable in molecular dynamics (MD) simulations. Thus, pressure-jump (P-jump)-induced protein refolding, if it could be made fast enough, would be ideally suited for comparison with MD. Although pressure denaturation perturbs secondary structure less than temperature denaturation, protein refolding after a fast P-jump is not necessarily faster than that after a temperature jump. Recent P-jump refolding experiments on the helix bundle λ-repressor have shown evidence of a <3 μs burst phase, but also of a ∼1.5 ms “slow” phase of refolding, attributed to non-native helical structure frustrating microsecond refolding. Here we show that a λ-repressor mutant is nonetheless capable of refolding in a single explicit solvent MD trajectory in about 19 μs, indicating that the burst phase observed in experiments on the same mutant could produce native protein. The simulation reveals that after about 18.5 μs of conformational sampling, the productive structural rearrangement to the native state does not occur in a single swift step but is spread out over a brief series of helix and loop rearrangements that take about 0.9 μs. Our results support the molecular time scale inferred for λ-repressor from near-downhill folding experiments, where transition-state population can be seen experimentally, and also agrees with the transition-state transit time observed in slower folding proteins by single-molecule spectroscopy.

Single-Photon Generation by Electron Beams

We propose a drastically new method for generating single photons in a deterministic way by interaction of electron beams with optical waveguides. We find a single swift electron to produce a guided photon with large probability. The change in energy and propagation direction of the electron reveals the creation of a photon, with the photon energy directly read from the energy-loss spectrum or the beam displacement. Our study demonstrates the viability of deterministically creating single guided photons using electron beams with better than picosecond time uncertainty, thus opening a new avenue for making room temperature, heralded frequency-tunable sources affordable for scientific and commercial developments.

Single swift heavy ion-induced trail of discontinuous nanostructures on SiO 2 surface under grazing incidence

Some recent results concerning swift heavy ion irradiation of thin SiO 2 layers on Si under normal incidence irradiation leading to the formation of nanodots at the interface between the SiO 2 film and the Si substrate or at the SiO 2 surface are summarized. Moreover, we report observation of discontinuous and elongated tracks at the SiO 2 surface after grazing incidence irradiation of SiO 2–Si structures with fast heavy ion. A characterization of these nanostructures by means of Atomic Force Microscopy (AFM) has been performed. The present results are of major importance with regard to the development of emerging nanoelectronic devices and systems.

The Mountaineers Learning Marksmanship

FEATURED AUTHOR THE MOUNTAINEERS LEARNING MARKSMANSHIP Thomas Wolfe "Lootenant," says the mountaineer with a deceptive look ofinnocence, "I think I know what you're tryin' to teach these fellers here?—with a look of pitying contempt at his beknighted companions, as if their ignorance was past his comprehension—"Now ain't it this'—the mountaineer went on gently, at the same time taking the rifle from his superior's hands—"Ain't you tryin' to tell 'em that they ought to shoot a gun like this?"—and with these words, and with a single movement, he brought the rifle to his shoulder and, without sighting, hit the bullseye at the heart. "Why I—" the lieutenant flinched, red as a ripe tomato on the farm. "Whyhell, no,Jim"—anothermountaineernowinterposed—You ain't got it right at all—what the /oo-tenant has been tryin' to tell you is that you ought to take a gun"—here he took the rifle from his comrade—"an' shoot it like this"—with these words he took a single swift look at the target and then shot from his hip a ringing bullseye a trifle closer to the centre ofthe target—ifthat were possible—than his comrade's—"Ain't that what you're tryin' to tell us, lootenant?" he said innocently, as he turned to his superior officer. "Why I—No!" the lieutenant shouted "that is decidedly not what I'm saying—that is not the way to do it—what you ought to do—" "Here, lootenant," a third mountaineer now quietly put in—"you let me tell 'em; this crowd here's so dumb they wouldn't understand you ifyou drawed a picksher fer 'em—Now you fellers look at me," this third man said quietly and authoritatively, as he took possession of the rifle "—what the lootenant's been tryin' to tell you all along is that when you shoot a gun you ought to do improper—now you take the gun like this—ain't that right, loo-tenenat?"— "Why, er—you bring—" "You bring it up like this—am I right or wrong, loo-tenanñ—" "Why, er—in a way—" "Now you aim the gun like this—ain't that the way you do it, loo-tenant? — " "Why, er—" "And then you pull the trigger"—with these words he shot three times and missed completely every time. "Hell," said the mountaineer, as he handed the rifle back to his superior—"you fellers are so dumb you don't know enough to come out of the rain—I knowed what the lootenant was talkin about the minute he showed me." Deputies and revenuers ...

Copper nanowires electrodeposited in etched single-ion track templates

The replication of single-ion track templates opens up the possibility of accessing electrical properties of nanowires without using lithographic techniques. Polycarbonate foils of 30-μm thickness were irradiated with single swift heavy ions (e.g. Au 11.4 or Xe 8.3 MeV/nucleon). By controlled one-sided etching of the damage trail caused by the ion, templates containing a single conical pore were prepared. The narrow pore openings had diameters down to 25 nm and opening angles up to 2°. By electrochemical deposition of copper, single conical wires were obtained. The electric current recorded during electrodeposition reflects the geometry of the pore. The wires were provided with electrical contacts. Current–voltage measurements confirmed that their resistance was ohmic. The wires could withstand a maximum current density above 108 A/cm2.

Determination of charge states of single swift heavy projectiles by high-energy delta-electrons

The effective charge state is an important particle parameter which is required for the calculation of many effects concerning the interaction between radiation and matter such as an estimate of the radial dose of swift heavy projectiles, stopping power and so on. A new method for the determination of effective charge states of heavy ions is based on the measurement of the number of high-energy delta-electrons which are ejected from a target by the penetrating ion. These electrons are detectable with a CCD-detector and their number can be correlated to the effective charge state of the projectile for known particle velocities. This method is even applicable to operation with single swift heavy ions within statistical bounds.

Detection of δ-electron events in charge coupled devices: a fingerprint of single swift heavy ions

Charge Coupled Devices, an arrangement of a few 100 000 photo-electric cells on a plane, allow the spatially and temporally resolved detection of single swift heavy ions and δ-electrons emitted by projectile-target-interactions from a target foil mounted at a distance of 500 μm above the microchip. This detector system is read out by standard TV technique and the signal is digitized for further processing by image analysis. The δ-electrons can be observed as a halo around the hit of the ion on the corresponding TV frame. The appearance of these halos is determined by the ion parameters velocity and effective charge. Vice versa the δ-electron halos provide information on the projectile within the bounds of the δ-electron statistics. This effect has been described in detail by an appropriate nuclear track structure model, which comprises production, transport and detection of δ-electrons as independent processes. First model calculations have been confirmed by experimental data.

Detection of single swift heavy ions with a system based on charge coupled devices

Charge Coupled Devices (CCDs), an arrangement of a few 100 000 photo-electric cells on a plane able to store the charge carriers liberated by the penetration of a particle, were applied for radiobiological investigations with single swift heavy ions performed at accelerators. For the extension of these experiments to unknown radiation fields, during space flights for instance, the projectile parameters energy and atomic number have to be estimated. For this purpose the angular distribution of δ-electrons is analyzed, which are ejected from a foil arranged over the microchip by heavy projectiles and which are detected in the CCD. The feasibility of this method regarding energy resolution and projectile identification is discussed.

Near‐surface circulation of the Nordic seas as measured by Lagrangian drifters

In the period June 1991 to August 1993, 107 Argos tracked, drifters drogued to 15 m depth, were released in the Nordic seas (or Greenland, Iceland, and Norwegian Seas). The drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the Iceland‐Faroe Frontal zone and of the Norwegian coast and along the continental margins and their extensions to the Barents Sea and Spitsbergen. The Norwegian Atlantic Current is composed of three distinct streams (two continental margin and one coastal branches) which join into one single swift mean current west of the Lofoten and Vesterålen Islands, where the strongest measured currents are in excess of 110 cm s−1. In addition to the general cyclonic gyre circulation in the Nordic seas, the drifters indicate smaller cyclonic circulation patterns in all the major subbasins, i.e., the Iceland plateau, the Norwegian, the Lofoten, and the Greenland basins. No surface signature of the East Icelandic Current is disclosed by the drifters. Interpolated and low‐pass‐filtered position data were used to construct maps of 15‐m‐depth ensemble mean velocity, velocity variability, and residence time. Vigorous eddy fields are dominant in the strong currents and in the Lofoten basin. Eulerian correlations indicate that they tend to propagate to the west. In contrast, the Iceland plateau appears quiescent, both in the mean and eddy velocities. Single‐particle diffusivities are computed and are found to be in the range 1–7 × 107 cm2 s−1. The corresponding Lagrangian timescale and space scale are 1–3 days and 10–40 km, respectively. These Lagrangian drifter measurements compose the first basin‐scale, accurate near‐surface velocity data set of the Nordic seas.

Centralisation and Decentralisation in Japan's ‘Information Society’

Not long after midnight on 29 November 1985, a small group of guerillas belonging to the radical organisation Chukaku-ha, slashed the underground communications cables serving the Japan National Railways network in Tokyo and Osaka. They were protesting at government plans to privatise the railway system, but their action was perhaps more important for the way in which it focused attention on a quite different economic and social issue. In a single swift sortie, a handful of people had been able to prevent the movement of some 4.5 million computers, and bring the life of one of the world's largest cities to a temporary halt. Nothing could more effectively have demonstrated the great and growing dependence of contemporary social systems on the communication of information, not only between individual and individual, but also between computer and computer.

Irving Langmuir, 1881-1957

In the winter of 1942, as retiring President of the American Association for the Advancement of Science, Irving Langmuir addressed the membership on the topic ‘Science, commonsense and decency’. He was concerned with the interaction of scientific progress and human endeavour and took the opportunity to reveal his own ideas concerning problems of human behaviour and morality. He recognized two categories of phenomena in modern physics which he termed convergent and divergent phenomena. He included among the convergent phenomena all those fluctuating details of individual atoms and molecules which average out giving a result that converges to a definite state. Many of the phenomena of classical physics belong in the convergent category. To a second class he assigned the divergent phenomena where, from a small beginning, increasingly large effects are produced. Quantum physics includes many such phenomena. Langmuir chose as an illustrative example the Wilson cloud-chamber experiment. Here, a single swift particle, say an alpha particle, whose release from its parent is unpredictable as to time and direction, subject only to the laws of chance, in its passage through the chamber leaves a trail of ions. If the chamber atmosphere be super-saturated, droplets are formed; illumination renders these visible and photography can record the multiple divergent consequences from a single event, the release of the swift particle. In further development of this theme of divergence Langmuir went on to state that ‘when we consider the nature of human affairs it is to me obvious that divergent phenomena frequently play a role of vital importance’. Langmuir’s birth on 31 January 1881 comes within the category of his divergent phenomena, from which beginning profound effects on the development of physico-chemical science finally resulted.

The Migration of Swifts

ON the morning of Friday, August 10, I witnessed a large flight of Swifts travelling westward along the Sussex coast. The birds were passing this place in a continuous though thin stream for several hours; I saw them myself from 10 a.m. when I first visited the shore, and watched them till 12 noon. A few birds were also noted travelling in the same direction between 5 p.m. and 6 p.m. The day was bright but showery, and a fresh W.N.W. breeze was blowing at the time, so that the birds were flying almost against the wind; they flew low, seldom rising fifteen feet in the air, and often passing within two feet of my head as I lay on the shingle; they kept to the coast-line and for the most part over the top of the fringe of tamarisks that here stretch for miles just above the shingle. Since that day I have not seen a single Swift in the neighbourhood, in spite of having travelled on my bicycle as far west as the mouth of Chichester Harbour along the coast, and to various places north of this line as far as Chichester and Arundel inland. It would be interesting to know if other observers witnessed any similar flights on August 10, and also if Swifts are still to be seen in any places in our islands at the present time. I have on two previous occasions seen Swifts arrive on the east coast of Norfolk as late as the first week in September (after a complete dearth of the birds for some three weeks), and depart again after a few days' sojourn—these perhaps are migrants from the European continent. As many of your readers are now doubtless at the seaside, it seems a favourable opportunity to ask them to keep their eyes open and record any facts that they may observe bearing on the movements of these birds.