External Radio-frequency Field Research Articles

Transition to a Magnon Bose–Einstein Condensate

Parameters of the transition from classical dynamics of spin waves to the formation of a coherent magnon Bose–Einstein condensate have been obtained experimentally for the first time. The studies are performed on an yttrium iron garnet film beyond the radio frequency excitation region; thus, the coherent state of magnons is an eigenstate rather than a state induced by an external radio frequency field. The critical magnon density at the formation of the Bose–Einstein condensate is in good agreement with a theoretically predicted value. The transition is obtained at room temperature, which is possible owing to a small mass of magnons and their high density.

Electrospun PCL/PVA Coaxial Nanofibers with Embedded Titanium Dioxide and Magnetic Nanoparticles for Stabilization and Controlled Release of Dithranol for Therapy of Psoriasis

Dithranol is one of the oldest and most efficient drugs used in the treatment of psoriasis. One of the challenges with using dithranol is its photostability, because it easily degrades when exposed to light. This study investigated the potential of coaxial core-sheath PCL/PVA nanofibers as a dual-functional system for enhancing dithranol photostability and remote-controlled drug delivery for psoriasis therapy. We have shown that coaxial nanofibers with titanium oxide nanoparticles (reflecting and absorbing ultra-violet light) in the PVA-based sheath part of the nanofibers can increase dithranol photostability. Incorporation of dithranol and magnetic nanoparticles into a PCL-based core of the nanofibers enables dithranol release control via an external radio-frequency field. The application of a radio-frequency field generates heat that can be used to control the release rate of drugs. Our approach therefore offers a non-invasive and remotely controlled drug release system that hold promise for the development of new topical formulations for psoriasis treatment using dithranol.

Engineered Magnetization Dynamics of Magnonic Nanograting Filters

Magnonic crystals and gratings could enable tunable spin-wave filters, logic, and frequency multiplier devices. Using micromagnetic models, we investigate the effect of nanowire damping, excitation frequency and geometry on the spin wave modes, spatial and temporal transmission profiles for a finite patterned nanograting under external direct current (DC) and radio frequency (RF) magnetic fields. Studying the effect of Gilbert damping constant on the temporal and spectral responses shows that low-damping leads to longer mode propagation lengths due to low-loss and high-frequency excitations are also transmitted with high intensity. When the nanowire is excited with stronger external RF fields, higher frequency spin wave modes are transmitted with higher intensities. Changing the nanowire grating width, pitch and its number of periods helps shift the transmitted frequencies over super high-frequency (SHF) range, spans S, C, X, Ku, and K bands (3–30 GHz). Our design could enable spin-wave frequency multipliers, selective filtering, excitation, and suppression in magnetic nanowires.

Biomimetic Magnetic Nanostructures: A Theranostic Platform Targeting Lipid Metabolism and Immune Response in Lymphoma.

B-cell lymphoma cells depend upon cholesterol to maintain pro-proliferation and pro-survival signaling via the B-cell receptor. Targeted cholesterol depletion of lymphoma cells is an attractive therapeutic strategy. We report here high-density lipoprotein mimicking magnetic nanostructures (HDL-MNSs) that can bind to the high-affinity HDL receptor, scavenger receptor type B1 (SR-B1), and interfere with cholesterol flux mechanisms in SR-B1 receptor positive lymphoma cells, causing cellular cholesterol depletion. In addition, the MNS core can be utilized for its ability to generate heat under an external radio frequency field. The thermal activation of MNS can lead to both innate and adaptive antitumor immune responses by inducing the expression of heat shock proteins that lead to activation of antigen presenting cells and finally lymphocyte trafficking. In the present study, we demonstrate SR-B1 receptor mediated binding and cellular uptake of HDL-MNS and prevention of phagolysosome formation by transmission electron microscopy, fluorescence microscopy, and ICP-MS analysis. The combinational therapeutics of cholesterol depletion and thermal activation significantly improves therapeutic efficacy in SR-B1 expressing lymphoma cells. HDL-MNS reduces the T2 relaxation time under magnetic resonance imaging (MRI) more effectively compared with a commercially available contrast agent, and the specificity of HDL-MNS toward the SR-B1 receptor leads to differential contrast between SR-B1 positive and negative cells suggesting its utility in diagnostic imaging. Overall, we have demonstrated that HDL-MNSs have cell specific targeting efficiency, can modulate cholesterol efflux, can induce thermal activation mediated antitumor immune response, and possess high contrast under MRI, making it a promising theranostic platform in lymphoma.

Magnetic and heating aptitudes of PEG coated [formula omitted] and [formula omitted] mediators towards hyperthermia methodology

In the present study functionalized mediator of Lanthanum strontium manganite (LSMO) has been investigated for magnetic fluid hyperthermia (MFH) applications. Perovskite structured (La1−xSrxMnO3) employing two Sr concentrations (x = 0.27 & 0.33) were attempted to coat with long chain structured polymer named Polyethylene glycol (PEG- 6000 g/mol) by adopting novel concentrations (5% & 14% w/v) in order to assess a detailed comparison of the effect of concentration of same coating material on two different LSMO's series. The Citrate-gel route was adopted to synthesize LSMOs nanoparticles (NPs). XRD revealed the super-paramagnetic (SPM) nature of synthesized NPs showing an approximate crystallite size of ∼17 nm. The LSMOs tailored with PEG showed an effective bonding of polymer with NPs exhibited by FTIR spectra. The magnetic parameters of coated NPs subjected to VSM at room temperature displayed an appreciable saturation magnetization and very slight coercivity owing to their SPM behaviour. During each synthesis, the relative proportions of polymer attached to LSMOs were evaluated through TGA analysis accompanied by DTA studies showing successive decomposition processes. The induction heating behaviours of NPs under an external radio frequency field displayed quite an appreciable approach for required Hyperthermia efficacy in the required range of 40–60 °C. Besides this, the coated NPs were dispersed in normal saline as an innovative try forming a ferro-fluid (∼19 mg/ml) and showed considerable approach towards induction heating for the destruction of cancerous cells employing hyperthermia methodology.

Experimental emulation of quantum non-Markovian dynamics and coherence protection in the presence of information backflow

We experimentally emulate, in a controlled fashion, the non-Markovian dynamics of a pure dephasing spin-boson model at zero temperature. Specifically, we use a randomized set of external radio-frequency fields to engineer a desired noise power-spectrum to effectively realize a non-Markovian environment for a single NMR qubit. The information backflow, characteristic to the non-Markovianity, is captured in the nonmonotonicity of the decoherence function and von Neumann entropy of the system. Using such emulated non-Markovian environments, we experimentally study the efficiency of the Carr-Purcell-Meiboom-Gill dynamical decoupling (DD) sequence to inhibit the loss of coherence. Using the filter function formalism, we design optimized DD sequences that maximize coherence protection for non-Markovian environments and study their efficiencies experimentally. Finally, we discuss DD-assisted tuning of the effective non-Markovianity.

The TRAPSENSOR facility: an open-ring 7 tesla Penning trap for laser-based precision experiments

A Penning-trap facility for high-precision mass spectrometry based on a novel detection method has been built. This method consists in measuring motional frequencies of singly-charged ions trapped in strong magnetic fields through the fluorescence photons from laser-cooled 40Ca+ ions, to overcome limitations faced in electronic single-ion detection techniques. The key element of this facility is an open-ring Penning trap coupled upstream to a preparation Penning trap similar to those used at Radioactive Ion Beam facilities. Here we present a full characterization of the trap and demonstrate motional frequency measurements of trapped ions stored by applying external radiofrequency fields in resonance with the ions’ eigenmotions, in combination with time-of-flight identification. The infrastructure developed to observe the fluorescence photons from 40Ca+, comprising the 12 laser beams and the optical system to register the image in a high-sensitive CCD sensor, has been proved by taking images of the trapped and cooled 40Ca+ ions. This demonstrates the functionality of the proposed laser-based mass-spectrometry technique, providing a unique platform for precision experiments with implications in different fields of physics.

Performance study of aluminum shielded room for ultra-low-field magnetic resonance imaging based on SQUID: Simulations and experiments**Project supported in part by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB04020200) and in part by the National Natural Science Foundation of China (Grant No. 11204339).

The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging (ULF MRI) based on the superconducting quantum interference device (SQUID). The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio (SNR) and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses (SE) of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m × 1.5 m × 2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance (NMR) signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields.

Cumulants and waitingtime distribution of the photon emission from driven BaF molecule

In this paper, we consider a single BaF molecule driven by an external field. When the symmetry is broken, the states of the BaF molecule demonstrate the permanent dipole moments. An external laser field to excite BaF molecule transition from its ground state to its excited state, and a radio frequency field couple with the permanent dipole moment of the BaF. The first order and second order cumulants of the emission photons and the waiting time distribution are studied via the recently developed generating function approach, which is very convenient to study the counting statistics and the corresponding probability distributions. The results demonstrate that the radio frequency field could help the BaF molecule to absorb photons from the driving field. The second and third order waiting time distributions oscillate with the evolution time, which reflects the states oscillating with the external radio frequency field.

Gold nanoparticle-based sensors activated by external radio frequency fields.

A novel molecular beacon (a nanomachine) is constructed that can be actuated by a radio frequency (RF) field. The nanomachine consists of the following elements arranged in molecular beacon configuration: a gold nanoparticle that acts both as quencher for fluorescence and a localized heat source; one reporter fluorochrome, and; a piece of DNA as a hinge and recognition sequence. When the nanomachines are irradiated with a 3 GHz RF field the fluorescence signal increases due to melting of the stem of the molecular beacon. A control experiment, performed using molecular beacons synthesized by substituting the gold nanoparticle by an organic quencher, shows no increase in fluorescence signal when exposed to the RF field. It may therefore be concluded that the increased fluorescence for the gold nanoparticle-conjugated nanomachines is not due to bulk heating of the solution, but is caused by the presence of the gold nanoparticles and their interaction with the RF field; however, existing models for heating of gold nanoparticles in a RF field are unable to explain the experimental results. Due to the biocompatibility of the construct and RF treatment, the nanomachines may possibly be used inside living cells. In a separate experiment a substantial increase in the dielectric losses can be detected in a RF waveguide setup coupled to a microfluidic channel when gold nanoparticles are added to a low RF loss liquid. This work sheds some light on RF heating of gold nanoparticles, which is a subject of significant controversy in the literature.

The interconversion of the radial motional modes of an ion in a Penning trap mass spectrometer by 4n‐polar external radio frequency fields (n = 1,2,3,4)

In Penning trap mass spectrometry ion masses are determined by measuring the free cyclotron frequency via the resonant conversion of the magnetron into the cyclotron motional mode, induced by the interaction with an external radio‐frequency field. With octupolar rf‐fields of frequency the mass resolution has been improved by more than an order of magnitude as compared to conventional quadrupolar fields of frequency and with the same pulse duration. This result raises the question what one might expect from using 12‐polar rf‐fields with frequency or even 16‐polar rf‐fields with frequency .In this paper the theoretical model for the interconversion of the radial modes by quadrupolar and octupolar rf‐fields is generalized to general 4n‐polar fields. As in the earlier work the complex amplitudes of the cyclotron and magnetron oscillators are used as dynamical variables and the Hamiltonian equations of motion are reformulated in terms of Bloch vector components. The resulting non‐linear differential equations can be solved numerically.Results are presented on excitation functions (conversion at the exact resonance frequency) and on conversion line shapes (dependence of conversion on the detuning parameter). The most important observation is the decrease of the resonance width by a factor of 2 × 103 as one passes from quadrupolar () to 12‐polar () and 16‐polar () excitation.

Remote control of diffusion from magnetic hollow silica microspheres

Composite hollow core silica/iron oxide microparticles with the ability to store an encapsulated payload and release a defined quantity “on demand” by the application of a radiofrequency magnetic field were prepared. The microparticles possessed a mesoporous silica shell with iron oxide nanoparticles bound to the external silica surface by electrostatic interaction. The size, morphology and stability of the composite particles were systematically investigated and the effect of ironoxide:silica ratio on their heating rate and the release kinetics of a model compound (vitamin B12) was determined. The composite particles were stable in time and had a high heating ability in the radiofrequency magnetic field, achieving a temperature rise of several 10’s°C per minute. Thanks to the high heating rate, external radiofrequency field was shown to be an effective trigger mechanism for externally controlled diffusion of encapsulated material from within the hollow core at an arbitrary on–off sequence.

Theoretical investigations of different excitation modes for Penning trap mass spectrometry

In Penning trap mass spectrometry the motion of trapped ions is manipulated by external radio-frequency fields. This paper describes a general theoretical framework to classify the various types of excitation of the ion's motional modes, to identify the resonance frequencies, and to find the effective interaction Hamiltonians which are valid in the vicinity of the resonances. Instead of Cartesian or cylindrical coordinates and momenta our theoretical approach uses the complex oscillator amplitudes of the cyclotron, magnetron, and axial oscillators as its basic dynamical variables. Equations of motion are set up, which can be simplified in the vicinity of resonances by the resonating wave approximation. Explicit analytical solutions of these equations of motion are obtained for dipolar and quadrupolar excitation. Results are stated as functions of a dimensionless evolution parameter and a dimensionless detuning parameter. The conversion of magnetron into cyclotron motion by a quadrupolar field using the two-pulse Ramsey technique is analyzed as an interference phenomenon between two complex amplitudes describing these motional modes. For octupolar excitation the equations of motion are transformed into a set of three ordinary differential equations which are amenable to numerical solution in a straightforward way. Some results on the line shapes for the conversion of magnetron into cyclotron motion by octupolar excitation are given. Simultaneous excitation of the ion motion at two different resonance frequencies is briefly discussed, using the example of dipole excitation of the magnetron motion and conversion of magnetron into cyclotron motion by quadrupolar excitation. Finally modifications due to frictional damping are reviewed.

Stability of antibody-conjugated gold nanoparticles in the endolysosomal nanoenvironment: implications for noninvasive radiofrequency-based cancer therapy

The use of noninvasive radiofrequency (RF) electric fields as an energy source for thermal activation of nanoparticles within cancer cells could be a valuable addition to the emerging field of nano-mediated cancer therapies. Based on investigations of cell death through hyperthermia, and offering the ability for total-body penetration by RF fields, this technique is thought to complement and possibly outperform existing nano-heat treatments that utilize alternative heat production via optical or magnetic stimuli. However, it remains a challenge to understand fully the complex RF-nanoparticle-intracellular interactions before full system optimization can be engineered. Herein we have shown that liver cancer cells can selectively internalize antibody-conjugated gold nanoparticles (AuNPs) through receptor-mediated endocytosis, with the nanoparticles predominantly accumulating and aggregating within cytoplasmic endolysosomes. After exposure to an external RF field, nonaggregated AuNPs absorbed and dissipated energy as heat, causing thermal damage to the targeted cancer cells. We also observed that RF absorption and heat dissipation is dependent on solubility of AuNPs in the colloid, which is pH dependent. Furthermore, by modulating endolysosomal pH it is possible to prevent intracellular AuNP aggregation and enhance thermal cytotoxicity in hepatocellular cancer cells. From the Clinical EditorGold nanoparticles absorb energy from RF fields and can exert hyperthermic effects leading to cell death. Combining this known effect with antibody-based targeting of the nanoparticles, selective cancer specific hyperthermia induced cell death therapies can be designed, as demonstrated in this article.

ON THE RELATIVE “TRANSPARENCY” OF GAS-PHASE CORONENE MOLECULES TO LOW-ENERGY ELECTRONS: EFFECTS ON THE INTERSTELLAR MEDIUM

Free, gas-phase polycyclic aromatic hydrocarbons (PAHs) are understood to play an important role in the interstellar medium (ISM), as they are thought to significantly contribute to both diffused and unidentified infrared interstellar bands. They are also considered fundamental blocks of the interstellar dust, whose nature has important implications for a plethora of physical and chemical nanoscopic processes within the ISM. Since free electrons represent a versatile alternative way to transport energy in the interstellar space, in this paper we compute from quantum scattering methods the angular redistributions of free electrons by gas-phase coronene molecules, the latter of which are believed to be one of the most representative PAHs, in order to assess their role in describing the efficiency of electron deflection by this molecule. The associated rates can provide useful information about the coupling mechanism between external radio-frequency fields and complex molecular plasmas containing neutral and ionized PAHs. They can also yield information on the possible presence of such species in the dust phase of the medium.

Intracellular gold nanoparticles enhance non-invasive radiofrequency thermal destruction of human gastrointestinal cancer cells

BackgroundNovel approaches to treat human cancer that are effective with minimal toxicity profiles are needed. We evaluated gold nanoparticles (GNPs) in human hepatocellular and pancreatic cancer cells to determine: 1) absence of intrinsic cytotoxicity of the GNPs and 2) external radiofrequency (RF) field-induced heating of intracellular GNPs to produce thermal destruction of malignant cells. GNPs (5 nm diameter) were added to 2 human cancer cell lines (Panc-1, Hep3B). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and propidium iodide-fluorescence associated cell sorting (PI-FACS) assessed cell proliferation and GNP-related cytotoxicity. Other GNP-treated cells were exposed to a 13.56 MHz RF field for 1, 2, or 5 minutes, and then incubated for 24 hours. PI-FACS measured RF-induced cytotoxicity.ResultsGNPs had no impact on cellular proliferation by MTT assay. PI-FACS confirmed that GNPs alone produced no cytotoxicity. A GNP dose-dependent RF-induced cytotoxicity was observed. For Hep3B cells treated with a 67 μM/L dose of GNPs, cytotoxicity at 1, 2 and 5 minutes of RF was 99.0%, 98.5%, and 99.8%. For Panc-1 cells treated at the 67 μM/L dose, cytotoxicity at 1, 2, and 5 minutes of RF was 98.5%, 98.7%, and 96.5%. Lower doses of GNPs were associated with significantly lower rates of RF-induced thermal cytotoxicity for each cell line (P < 0.01). Cells not treated with GNPs but treated with RF for identical time-points had less cytotoxicity (Hep3B: 17.6%, 21%, and 75%; Panc-1: 15.3%, 26.4%, and 39.8%, all P < 0.01).ConclusionWe demonstrate that GNPs 1) have no intrinsic cytotoxicity or anti-proliferative effects in two human cancer cell lines in vitro and 2) GNPs release heat in a focused external RF field. This RF-induced heat release is lethal to cancer cells bearing intracellular GNPs in vitro.

Effect of an arbitrarily directed permanent magnetic field on the dynamic susceptibility of a superparamagnetic particle under the conditions of stochastic resonance

Theoretically, based on the approximation of discrete orientations, the effect of thermal stochastic resonance is considered for a superparamagnetic particle with magnetic anisotropy of the “easy axis” type in view of an additional external permanent magnetic field applied at an arbitrary angle relative to the easy magnetization axis. The dynamic susceptibility has been calculated for a single-domain iron particle under the conditions of its modulation by a weak external radio-frequency field at various absolute values and directions of the additional permanent magnetic field vector.

An autonomous bladder pressure monitoring system

This paper reports on the development of an autonomous monitoring system, capable of continuously measuring the pressure inside the bladder. The capsule features wireless bi-directional communication and can be inductively powered anywhere inside the bladder. Short-circuiting the resonant LC tank for the data transmission maximizes the operating range of the passive telemetry. A novel clock extraction method is presented, based on lock-in of a Schmitt-trigger oscillator into the external radio-frequency field. A prototype was built using only discrete components. The system measures the pressure with a resolution of 0.04 kPa at a sampling rate of 10 Hz.

Endoluminal Thermal Occlusion of the Ureter with the Electromagnetic Field-Focusing Device

The authors attempted ureteral occlusion by means of heat application in nine ureters (24 sites) of New Zealand White rabbits with the electromagnetic field-focusing (EFF) device. The EFF device generates heat at the tip of a grounded probe by focusing eddy currents that have been induced within the tissues by an external radio-frequency field. The power settings were varied from 30 to 150 W. Heat was applied at multiple sites in each ureter. Immediate functional occlusion was seen in all nine ureters. Long-term complete occlusion was seen in six ureters at power settings ranging from 40 to 150 W, while long-term partial occlusion was seen in two ureters at 30-50 W. All sites at 30 W resulted in partial occlusions. Perforation of the ureter resulted in urinoma formation in one ureter at a site that was treated with 150 W. The EFF device can be used to endoluminally occlude the ureter by causing a fibrotic reaction to thermal injury. The effective power range for this application appears to be 40-100 W.

Enhanced nuclear magnetism: some novel features and prospective experiments

This review of enhanced nuclear magnetism discusses a number of features not previously considered, with special reference to new experiments that use dynamic methods to produce high nuclear polarization, followed by adiabatic demagnetization in the rotating frame (a. d. r. f.) to produce nuclear ordered states that may be investigated by the scattering of beams of neutrons. Section 2. The ‘enhancement’ of the nuclear moment arises from the electronic magnetization M I induced through the hyperfine interaction. It is shown that the spatial distribution of M I is the same as that of M H , the Van Vleck magnetization induced by an external field, provided that J is a good quantum number. The spatial distributions are not in general the same in Russell-Saunders coupling, e. g. in the 3d group. Section 3. The Bloch equations are extended to include anisotropic nuclear moments. Section 4. The ‘truncated’ spin Hamiltonian is derived for spin-spin interaction between enhanced moments. Section 5. A general cancellation theorem for second-order processes in spin-lattice relaxation is derived, showing that the intrinsic direct process must be of third order. The relaxation rate obeys an equation similar to that for Kramers electronic ions, but reduced as the fifth power of the resonance frequencies. The relaxation rates observed experimentally (except in very high fields) are ascribed to paramagnetic impurities, so that these can be used to produce dynamic nuclear polarization (d. n. p.). Section 6. The interactions of neutrons with the true nuclear moment μ I the Van Vleck moment M H , the ‘pseudonuclear’ moment M I and the ‘pseudomagnetic’ nuclear moment μ * I are discussed. It is shown that the four contributions can be observed separately by measurement of the form factor for neutron scattering as a function of temperature and direction of the applied magnetic field. Precession of the neutron spin in the ‘pseudomagnetic’ field H * is discussed with reference to the case of HoVO 4 , and an experiment on ‘pseudomagnetic resonance’ is proposed, in which the neutron spin is ‘flipped’ by resonance with the precessing H * of 169 Tm in TmPO 4 polarized by d. n. p. Section 7. Ordered states of enhanced nuclear moment systems are considered, together with the conditions under which they might be produced by a. d. r. f. following d. n. p. On the assumption that a transverse helical ordered structure can be created in TmPO 4 , a pseudomagnetic resonance experiment is suggested making use of 169 Tm, in which the neutron spin is flipped without the intervention of an external radio-frequency field.