and downstroke (12). This discrepancy with
previous studies might reflect an interesting
difference in the control of pitch and roll compared with yaw. It is also noteworthy that stroke
angle exerts a stronger influence over forces
and moments than either wing rotation or stroke
deviation. This finding is consistent with many
previous studies in tethered flight which show
that flies robustly modulate stroke amplitude in
response to sensory signals that elicit changes
in flight force (31), as well as roll, pitch, and
yaw (28, 32).
Our results indicate that flies escape from looming objects by exhibiting a rapid banked turn. The
motor basis of these rapid maneuvers are quite
distinct from those previously described in that the
change in direction is generated by a combination
of pitch and roll, requiring active torque and
countertorque generated by a fine-scaled, coordinated change in all aspects of wing motion. The
changes in heading during these maneuvers are
roughly 5 times as fast (5300° s−1) as those measured during voluntary saccadic turns (1000° s−1)
(33, 34), suggesting that this strategy provides the
animals with the fastest possible means for altering direction. Using the genetic and physiological
approaches available in the closely related species
D. melanogaster, it should be possible to elucidate
the neural circuitry and muscle physiology that
underlies these rapid behaviors.
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Acknowledgments: This work was supported by grants from
the Air Force Office of Scientific Research (FA9550-10-1-0368)
to M.H.D., the Paul G. Allen Family Foundation to M.H.D.,
Army Research Laboratory (DAAD 19-03-D-0004) to M.H.D.,
Swedish Research Council to F. T.M., and the Royal Physiographical
Society in Lund to F. T.M. We thank S. Safarik, X. Zabala,
and J. Liu for their technical support, and B. van Oudheusden
for co-supervising J.M.M. The data reported in this paper are
tabulated in the supplementary materials: The body and wing
kinematics data for all reported flight sequences, as well as
forces and torques from the robotic fly experiments, are
stored in Database S1, and the Fourier series coefficients
required to reconstruct the here analyzed wingbeat kinematics
(using eq. S1) are available in table S1.
Materials and Methods
Figs. S1 to S6
Movies S1 to S11
25 November 2013; accepted 11 March 2014
Ultrafast Switching to a Stable
Hidden Quantum State in an
L. Stojchevska,1,2 I. Vaskivskyi,1 T. Mertelj,1 P. Kusar,1 D. Svetin,1 S. Brazovskii,3,4 D. Mihailovic1,2,5*
Hidden states of matter may be created if a system out of equilibrium follows a trajectory to a
state that is inaccessible or does not exist under normal equilibrium conditions. We found such a
hidden (H) electronic state in a layered dichalcogenide crystal of 1T-TaS2 (the trigonal phase
of tantalum disulfide) reached as a result of a quench caused by a single 35-femtosecond laser
pulse. In comparison to other states of the system, the H state exhibits a large drop of electrical
resistance, strongly modified single-particle and collective-mode spectra, and a marked change
of optical reflectivity. The H state is stable until a laser pulse, electrical current, or thermal
erase procedure is applied, causing it to revert to the thermodynamic ground state.
In condensed matter systems, laser photoex- citation may temporarily destroy ground- state ordering; the system typically reverts
to the ground state in a few picoseconds, unless
it passes though a transient metastable state.
Such metastable states have been shown to
persist on time scales between 10−9 and 10−3 s
(1–9) before returning to the ground state by a
combination of thermal, electronic, and lattice
relaxation processes (2). Stability of photoinduced
states has been demonstrated in a manganite (6)
and in chalcogenide glasses (10), where switch-
ing occurs between neighboring equilibrium
thermodynamic states. Here, we report on bi-
stable switching to a hidden (H), spontaneously
ordered macroscopic quantum state whose prop-
erties are distinct from those of any other state in
the equilibrium phase diagram. The hidden state
transition (HST) occurs in a layered quasi–two-
dimensional chalcogenide 1T-TaS2 crystal, which
exhibits multiple competing ground states under
equilibrium conditions. Near Tc0 = 550 K, 1T-TaS2
forms an incommensurate (IC) charge density
wave (CDW) with an associated lattice distor-
tion. Upon cooling, these modulations sharpen
to form star-shaped polaron clusters (Fig. 1A).
Their ordering is thought to be responsible for a
variety of phases, causing a transition to a nearly
commensurate (NC) state for T < Tc1 = 350 K,
and a hysteretic first-order transition to a gapped
commensurate (C) phase near Tc2 = 183 K. Upon
1Department of Complex Matter, Jozef Stefan Institute, Jamova
39, Ljubljana SI-1000, Slovenia. 2Jozef Stefan International
Postgraduate School, Jamova 39, Ljubljana SI-1000, Slovenia.
3LPTMS-CNRS, UMR8626, Université Paris-Sud, F-91405
Orsay, France. 4International Institute of Physics, 59078-400
Natal, Rio Grande do Norte, Brazil. 5CENN Nanocenter, Jamova
39, Ljubljana SI-1000, Slovenia.
*Corresponding author. E-mail: firstname.lastname@example.org