LB12021ER
Cells, cancer and rare events
Enormous strides have been made towards understanding the molecular and
genetic origins of cancers. At the same time something of a mystery
remains in the incidence rate of lung cancer in ex-smokers. Detailed
analysis of the dynamics suggests that part of the mechanism at least
may have nothing to do with genetic changes in DNA. In this paper a
possible mechanism is examined, which the author terms "homeostatic
metastability". The idea is that the clinical appearance of cancer may
be a random, rare event arising from the collective behaviour of the
cells, a bit like the way bubbles appear in a fizzy drink or ice
crystals nucleate in supercooled water. At the moment, homeostatic
metastability remains an intriguing possibilitity, put forward as a
hypothesis to be supported or knocked down by experimental evidence. If
it should prove to be a factor in cancer though, it opens up interesting
possibilities for novel treatment regimes.
***
LG12379
First Bose-Einstein condensate of an alkaline earth element - Matter wave
meets optical atom clock
Bose-Einstein condensates (BECs) as a source of coherent matter waves have
been used in the past years for a variety of measurements in fundamental
quantum mechanics as well as a model system for solid state physics and
for quantum information. Most BECs are made from alkaline atoms sharing
one disadvantage: For optical transitions they have a broad line width
i.e. they can be excited not only by a single frequency but by frequencies
in a range of several megahertz. The energy uncertainty related to this
line width is large compared to typical energy scales in a BEC as
temperature, photon recoil, chemical potential, or trap level spacing.
For the first time, a BEC of alkaline earth atoms has been produced. The super-narrow intercombination lines of this class of atoms allow optical excitation
with high precision and make them candidates for optical clocks. Combining
this feature with the coherent matter wave of a BEC does not only promise
new measurements on matter light interaction but can also be used for
precision spectroscopy of the properties of a condensate or for new
interferometric sensors for various kinds of forces, e.g. gravity.
Friday, August 28, 2009
Thursday, August 27, 2009
LF12828
Broadband electromagnetic cloaking in the microwaves and visible
In our recent article “Broadband electromagnetic cloaking of long
cylindrical objects” (to appear in Physical Review Letters) we have
shown how very simple metallic parallel-plate structures can be used to
cloak or, in other words, to make “invisible” e.g. cylindrical metallic
objects. Two designs are presented: one operating in the microwave
region and the other in the visible part of the electromagnetic
spectrum.
Operation of both structures is confirmed with numerical
simulations and the microwave device is also realized and measured. The
results confirm that this new cloaking phenomenon can be realized with
very simple structures and the designed devices are shown to operate in
relatively wide frequency bands.
***
BE11444
Scientists Solve Mystery of Glass Flow
A popular urban legend concerns the apparent flow of stained glass windows in medieval cathedrals. This problem is of critical importance for modern industrial glass, particularly the ultra-thin glass sheets used in liquid crystal displays (LCDs), where such flow can lead to unwanted dimensional changes during the LCD manufacturing process. In a newly published paper, “Nonequilibrium viscosity of glass” (Phys. Rev. B), a trio of scientists have conducted the first-ever thorough investigation of viscous flow at temperatures below the glass transition. They present major advances in the underlying theory of nonequilibrium viscosity, developing a new model which accounts for the full thermal history dependence of glass flow behavior. Using an internally designed beam bending apparatus capable of accurate viscosity measurements well below the glass transition, the authors present a detailed validation study of Corning’s EAGLE XG glass, the most popular glass used in today’s large-scale LCD televisions. The new theory unveils a striking relationship between the history-dependent viscosity of the glass at low temperatures and the high-temperature viscosity of the equilibrium melt.
***
BTR1060BJ
Coiled Nanotubes
Carbon nanotubes are promising materials for the future. It would be
interesting to study what would happen when it is curved or coiled. In this
paper, we report that ring shaped nanotubes would behave differently than
straight ones. In our experiment, we investigate many rings with different
diameters using laser spectrum. We found that rings would show more peaks in
their spectra. The smaller, the more peaks. Usually graphene sheet have only
one peak in its Raman G band, when it is rolled up and forms a tube, there
would be two peaks in the G band. In our case, the tube is further rolled up
to form a ring and the number of peaks increases to six. This interesting
phenomenon may promote a deeper understanding of the mechanism of the spectrum
of carbon nanotubes and related materials like graphene and graphite.
Currently, we attribute the increasing of peak number with additional
curvature to the changes in electronic structures resulted by the residual
strain during the formation process of ring structures.
Broadband electromagnetic cloaking in the microwaves and visible
In our recent article “Broadband electromagnetic cloaking of long
cylindrical objects” (to appear in Physical Review Letters) we have
shown how very simple metallic parallel-plate structures can be used to
cloak or, in other words, to make “invisible” e.g. cylindrical metallic
objects. Two designs are presented: one operating in the microwave
region and the other in the visible part of the electromagnetic
spectrum.
Operation of both structures is confirmed with numerical simulations and the microwave device is also realized and measured. The
results confirm that this new cloaking phenomenon can be realized with
very simple structures and the designed devices are shown to operate in
relatively wide frequency bands.
***
BE11444
Scientists Solve Mystery of Glass Flow
A popular urban legend concerns the apparent flow of stained glass windows in medieval cathedrals. This problem is of critical importance for modern industrial glass, particularly the ultra-thin glass sheets used in liquid crystal displays (LCDs), where such flow can lead to unwanted dimensional changes during the LCD manufacturing process. In a newly published paper, “Nonequilibrium viscosity of glass” (Phys. Rev. B), a trio of scientists have conducted the first-ever thorough investigation of viscous flow at temperatures below the glass transition. They present major advances in the underlying theory of nonequilibrium viscosity, developing a new model which accounts for the full thermal history dependence of glass flow behavior. Using an internally designed beam bending apparatus capable of accurate viscosity measurements well below the glass transition, the authors present a detailed validation study of Corning’s EAGLE XG glass, the most popular glass used in today’s large-scale LCD televisions. The new theory unveils a striking relationship between the history-dependent viscosity of the glass at low temperatures and the high-temperature viscosity of the equilibrium melt.
***
BTR1060BJ
Coiled Nanotubes
Carbon nanotubes are promising materials for the future. It would be
interesting to study what would happen when it is curved or coiled. In this
paper, we report that ring shaped nanotubes would behave differently than
straight ones. In our experiment, we investigate many rings with different
diameters using laser spectrum. We found that rings would show more peaks in
their spectra. The smaller, the more peaks. Usually graphene sheet have only
one peak in its Raman G band, when it is rolled up and forms a tube, there
would be two peaks in the G band. In our case, the tube is further rolled up
to form a ring and the number of peaks increases to six. This interesting
phenomenon may promote a deeper understanding of the mechanism of the spectrum
of carbon nanotubes and related materials like graphene and graphite.
Currently, we attribute the increasing of peak number with additional
curvature to the changes in electronic structures resulted by the residual
strain during the formation process of ring structures.
Monday, August 24, 2009
August 24, 2009
EF10631
Effective bacterial micromixers
Scientists have discovered that commonly found bacteria such as Bacillus
Subtilis are in fact highly efficient mixers for the liquid they live
in. Thanks to original non-invasive optical coherence tomography (OCT)
developed by Imalux Corporation, OH, the scientists observed with
unprecedented precision the phenomena unfolding in the liquid containing
the bacteria. The measurements revealed up to 100-fold increase of
mixing and Oxygen intake rates due to coordinated swimming of the bacteria.
The study sheds a new light on possible survival mechanisms developed by
bacterial colonies under harsh conditions. In addition, the results are
important for fundamental and technological reasons, from understanding
collective motion in groups of interacting animals such as bird flocks
and fish schools to miniature bacteria-powered mixers and reactors.
Image illustrates three-dimensional distribution of bacteria obtained by
the OCT scan
***
LW10950AR
Space Time Sensors Juggling With Multiple Ultracold Atomic Waves
Thanks to their ability to measure time with an extreme accuracy, optical
atomic clocks are of great importance for modern physics [1]. The best
clocks to date control the atomic motion by trapping the sample within
optical lattices and then probe the atomic transition by shining on
these atoms a distinct laser of controlled frequency. In order to perform
both operations simultaneously and with the same laser field, we explore
in this paper a different strategy: using fine-tuned laser pulses, one can
perform a quantum juggling with a Bose-Einstein condensate and exploit the
resulting interferences to enhance the measurement sensitivity. The
condensate goes through an unusual levitation process: it is split into a
myriad of wave-packets exploring a network of paths, thereby experiencing
simultaneously a controlled diffusion in altitude and a localization in
momentum. Thanks to the chosen geometry, this proposal combines the best
aspects of optical clocks based on atom traps and on atom
interferometers. This system is also able to measure accelerations. It
represents an attractive alternative to current atom gravimeters and
atomic clocks.
***
LD12391
Quantum Limit for Probing Quantized Energy Levels of a Mechanical
Oscillator
Recent novel experiments with electromechanical and optomechanical
systems unveilpossibilities of exploring quantum behavior of a macroscopic mechanical oscillator. If energy levels of a mechanical oscillator were observed to be quantized, this will give us an unequivocal sign of quantumness of a macroscopic object. Motivated by the pioneering work of Thompson et al., we derive a standard quantum limit for observing energy quantization in systems with a mechanical oscillator coupled parametrically to external degrees of freedom. In order to successfully probe the quantized energy levels, the mechanical oscillator needs to strongly interact with the external degrees of freedom. In the case of optomechanical system, as intuitively expected, it requires zero-point motion of the oscillator to be comparable to the linear dynamical range of the optical system. This condition indicates the threshold when nonlinearity in the system plays a significant role. Interestingly, it is also the point where momentum kick by a single photon exceeds zero-point fluctuation of the oscillator momentum, allowing realization of macroscopic quantum supposition [3]. Therefore, if this condition is satisfied, many fascinating nonlinear and non-Gaussian properties of the optomechanical system will show up in the quantum regime.
***
LA12165Z
Making bright electron beams for compact x-ray lasers
A novel method to accomplish highly-brilliant electron beams required for coherent x-ray generation in a compact x-ray free-electron laser (XFEL) is presented. Since the nonlinearity of electron beam compression limits the attainable peak current, a correction cavity operated at a high-harmonic frequency of a main accelerator is conventionally used for nonlinearity compensation. However in a compact XFEL using a high-frequency main accelerator, a conventional scheme encounters a technological difficulty of an extremely high-frequency microwave system. In this paper, a novel nonlinearity correction scheme is proposed for a compact XFEL, in which an effective frequency up-conversion of a correction cavity obtained in the beam compression is directly used. As a result, the frequency of the correction cavity can be decreased to the same frequency as the main accelerator. Derived analytical formulae and simulations confirm the successful generation of highly-brilliant electron beams in a compact XFEL. This new scheme will become a key technique to downsize the scale of the facility, which is an essential issue for widespread application of coherent x-ray light sources.
***
LE12697
How perfect can graphene be?
We have identified the cyclotron resonance response of purest
graphene ever investigated, which can be found in nature on the surface of
bulk graphite, in form of decoupled layers from the substrate material.
Probing such flakes with Landau level spectroscopy in the THz range at
very low magnetic fields, we demonstrate a superior electronic quality of
these ultra-low density layers (close to 10^9 cm-2), expressed by the
carrier mobility in excess of 10^7 cm2/(V.s). These parameters set new and
surprisingly high limits for intrinsic properties of graphene and
represent an important challenge for further developments of current
graphene technologies. Graphene samples with mobilities comparable to the
nowadays highest-mobility semiconductor devices thus seem to be
achievable. Intriguingly, electronic states in such high-quality graphene
could be quantized into Landau levels by magnetic fields as low as the
field of the Earth.
Effective bacterial micromixers
Scientists have discovered that commonly found bacteria such as Bacillus
Subtilis are in fact highly efficient mixers for the liquid they live
in. Thanks to original non-invasive optical coherence tomography (OCT)
developed by Imalux Corporation, OH, the scientists observed with
unprecedented precision the phenomena unfolding in the liquid containing
the bacteria. The measurements revealed up to 100-fold increase of
mixing and Oxygen intake rates due to coordinated swimming of the bacteria.
The study sheds a new light on possible survival mechanisms developed by
bacterial colonies under harsh conditions. In addition, the results are
important for fundamental and technological reasons, from understanding
collective motion in groups of interacting animals such as bird flocks
and fish schools to miniature bacteria-powered mixers and reactors.
Image illustrates three-dimensional distribution of bacteria obtained by
the OCT scan
***
LW10950AR
Space Time Sensors Juggling With Multiple Ultracold Atomic Waves
Thanks to their ability to measure time with an extreme accuracy, optical
atomic clocks are of great importance for modern physics [1]. The best
clocks to date control the atomic motion by trapping the sample within
optical lattices and then probe the atomic transition by shining on
these atoms a distinct laser of controlled frequency. In order to perform
both operations simultaneously and with the same laser field, we explore
in this paper a different strategy: using fine-tuned laser pulses, one can
perform a quantum juggling with a Bose-Einstein condensate and exploit the
resulting interferences to enhance the measurement sensitivity. The
condensate goes through an unusual levitation process: it is split into a
myriad of wave-packets exploring a network of paths, thereby experiencing
simultaneously a controlled diffusion in altitude and a localization in
momentum. Thanks to the chosen geometry, this proposal combines the best
aspects of optical clocks based on atom traps and on atom
interferometers. This system is also able to measure accelerations. It
represents an attractive alternative to current atom gravimeters and
atomic clocks.
***
LD12391
Quantum Limit for Probing Quantized Energy Levels of a Mechanical
Oscillator
Recent novel experiments with electromechanical and optomechanical
systems unveilpossibilities of exploring quantum behavior of a macroscopic mechanical oscillator. If energy levels of a mechanical oscillator were observed to be quantized, this will give us an unequivocal sign of quantumness of a macroscopic object. Motivated by the pioneering work of Thompson et al., we derive a standard quantum limit for observing energy quantization in systems with a mechanical oscillator coupled parametrically to external degrees of freedom. In order to successfully probe the quantized energy levels, the mechanical oscillator needs to strongly interact with the external degrees of freedom. In the case of optomechanical system, as intuitively expected, it requires zero-point motion of the oscillator to be comparable to the linear dynamical range of the optical system. This condition indicates the threshold when nonlinearity in the system plays a significant role. Interestingly, it is also the point where momentum kick by a single photon exceeds zero-point fluctuation of the oscillator momentum, allowing realization of macroscopic quantum supposition [3]. Therefore, if this condition is satisfied, many fascinating nonlinear and non-Gaussian properties of the optomechanical system will show up in the quantum regime.
***
LA12165Z
Making bright electron beams for compact x-ray lasers
A novel method to accomplish highly-brilliant electron beams required for coherent x-ray generation in a compact x-ray free-electron laser (XFEL) is presented. Since the nonlinearity of electron beam compression limits the attainable peak current, a correction cavity operated at a high-harmonic frequency of a main accelerator is conventionally used for nonlinearity compensation. However in a compact XFEL using a high-frequency main accelerator, a conventional scheme encounters a technological difficulty of an extremely high-frequency microwave system. In this paper, a novel nonlinearity correction scheme is proposed for a compact XFEL, in which an effective frequency up-conversion of a correction cavity obtained in the beam compression is directly used. As a result, the frequency of the correction cavity can be decreased to the same frequency as the main accelerator. Derived analytical formulae and simulations confirm the successful generation of highly-brilliant electron beams in a compact XFEL. This new scheme will become a key technique to downsize the scale of the facility, which is an essential issue for widespread application of coherent x-ray light sources.
***
LE12697
How perfect can graphene be?
We have identified the cyclotron resonance response of purest
graphene ever investigated, which can be found in nature on the surface of
bulk graphite, in form of decoupled layers from the substrate material.
Probing such flakes with Landau level spectroscopy in the THz range at
very low magnetic fields, we demonstrate a superior electronic quality of
these ultra-low density layers (close to 10^9 cm-2), expressed by the
carrier mobility in excess of 10^7 cm2/(V.s). These parameters set new and
surprisingly high limits for intrinsic properties of graphene and
represent an important challenge for further developments of current
graphene technologies. Graphene samples with mobilities comparable to the
nowadays highest-mobility semiconductor devices thus seem to be
achievable. Intriguingly, electronic states in such high-quality graphene
could be quantized into Landau levels by magnetic fields as low as the
field of the Earth.
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