Undergo Phase Transitions Research Articles

Vanishing Confinement Regime in Terahertz HgTe Nanocrystals Studied under Extreme Conditions of Temperature and Pressure.

While HgTe nanocrystals (NCs) in the mid-infrared region have reached a high level of maturity, their far-infrared counterparts remain far less studied, raising the need for an in-depth investigation of the material before efficient device integration can be considered. Here, we explore the effect of temperature and pressure on the structural, spectroscopic, and transport properties of HgTe NCs displaying an intraband absorption at 10 THz. The temperature leads to a very weak modulation of the spectrum as opposed to what was observed for strongly confined HgTe NCs. HgTe NC films present ambipolar conduction with a clear prevalence of electron conduction as confirmed by transistor and thermoelectric measurements. Under the application of pressure, the material undergoes phase transitions from the zinc blende to cinnabar phase and later to the rock salt phase which we reveal using joint X-ray diffraction and infrared spectroscopy measurements. We discuss how the pressure existence domain of each phase is affected by the particle size.

Synthesis, characterization, and thermal and computational investigations of the l-histidine bis(fluoride) crystal

Nonlinear optical materials have been investigated recently due to their potential technological applications in information storage and communications. In this context, semi-organic crystals can effectively combine the desired nonlinear optical properties of amino acids with the promising mechanical and thermal properties of inorganic materials. In this work, we have synthesized and characterized a semi-organic crystal of the amino acid l-histidine and hydrofluoric acid and investigated the chemical interactions between the organic and inorganic moieties. The crystal of l-histidine bis(fluoride) has been produced by slow solvent evaporation and characterized by X-ray diffraction (XRD) crystallography and thermogravimetric and differential thermal analyses. The XRD conducted using the Rietveld method shows that the unit cell is orthorhombic with the P21212 space group and contains four l-histidine bis(fluoride) units. Both differential thermal analysis and temperature-dependent XRD show that the crystals are thermally stable up to 191°C and do not undergo phase transition. The computational Hirshfeld surface analysis of the crystal structure reveals the main intermolecular interactions. Density functional theory has been employed to calculate the ionic interaction energy and electrostatic potential maps and confirm the spontaneity of ionic association at 191°C. The combined experimental and computational results show that the thermal stability of the semi-organic l-histidine bis(fluoride) crystal makes it suitable for nonlinear optical applications in optical sensing and communication systems.Graphical abstract

Explosion Risks during Firefighting Operations in Storage Rooms and the Transport of Ammonium Nitrate-Based Fertilizers

Ammonium nitrate (AN) is a strong oxidizer that undergoes phase transitions and thermal decomposition at relatively low temperatures. This—as verified by historical facts—constitutes a challenge for the fire department during rescue operations. AN is also a highly reactive material widely used for the production of, i.a., fertilizers and explosives. The latter are popular not only in military applications but also in industrial ones, such as mining. They include ammonites and amatols utilized in coal mining, as well as Ammonium Nitrate Fuel Oil (ANFO) utilized in, i.a., rock mining. As a simple and cheap material, ANFO also tends to be used by terrorists. The spontaneous formation of an AN and polymers mixture—similar to ANFO in terms of composition and explosion force—was observed in fire conditions during previous research. At individual stages (from creation to exploitation), AN often comes into direct contact with various polymers. Polyolefins, in particular polyethylene (PE) and polypropylene (PP), are among the most popular groups of such materials. They are used for the production of, i.a., foil packaging and flexible intermediate bulk containers for the storage and transport of fertilizers. Despite the frequent mutual contact of these materials, there is little information in the literature on the interaction of AN and its polymer-made packaging in fire conditions. For this reason, it was decided to conduct a series of thermal analyses using Differential Scanning Calorimetry (DSC) to study the material behavior under the influence of high temperature. As it turns out in practice, the spontaneous formation of a mixture similar to ANFO—in terms of composition and explosion force—can be observed in fire conditions. Due to the results indicating a potentially explosive course of the reaction, laboratory tests on the macro scale were also carried out. The performed observations show that it may be necessary to create a procedure containing several different test methods in order to predict a mixture’s behavior during a fire and to define the appropriate guidelines for firefighting teams. Such guidelines would enable firefighters to prepare the right equipment during a firefighting operation and to develop a strategy based on the observed course of events.

The relative binding position of Nck and Grb2 adaptors impacts actin-based motility of Vaccinia virus.

Phosphotyrosine (pTyr) motifs in unstructured polypeptides orchestrate important cellular processes by engaging SH2-containing adaptors to assemble complex signalling networks. The concept of phase separation has recently changed our appreciation of multivalent networks, however, the role of pTyr motif positioning in their function remains to be explored. We have now investigated this parameter in the operation of the signalling cascade driving actin-based motility and spread of Vaccinia virus. This network involves two pTyr motifs in the viral protein A36 that recruit the adaptors Nck and Grb2 upstream of N-WASP and Arp2/3 complex-mediated actin polymerisation. Manipulating the position of pTyr motifs in A36 and the unrelated p14 from Orthoreovirus, we find that only specific spatial arrangements of Nck and Grb2 binding sites result in robust N-WASP recruitment, Arp2/3 complex driven actin polymerisation and viral spread. This suggests that the relative position of pTyr adaptor binding sites is optimised for signal output. This finding may explain why the relative positions of pTyr motifs are frequently conserved in proteins from widely different species. It also has important implications for regulation of physiological networks, including those undergoing phase transitions.

Heat transfer, energy conversion, and efficiency during cold discharge of a novel tetrabutylammonium bromide hydrate cold storage system

• External melting by internal heat exchange was used to study hydrate cold discharge. • Thermal buffering occurred due to energy balance caused by heat transfer. • Forced convection from gas disturbance reduced cold discharge time by 3 times. • Cold discharge efficiency can be maintained above 83 % under different conditions. • Time-efficiency number was proved to quantify the total cold discharge efficiency. Cold storage technologies using clathrate hydrates as working media have recently attracted more attention in the energy storage field because they undergo phase transitions with large latent heats and suitable temperatures for cold storage. However, the application of hydrate cold storage technologies is limited by the fact that the cold discharge mechanism is still unclear. Thus, this paper adopted the method of external melting by internal heat exchange to investigate the heat transfer, energy conversion and efficiency of a novel tetrabutylammonium bromide (TBAB) hydrate cold storage system during cold discharge. The system consisted of an internal circulating gas disturbance device and a metal spiral hydrate-on-coil heat exchanger. The heat transfer mechanism and cold discharge capacity, rate, and efficiency for different cold charge temperatures, flow rates and disturbance modes were compared and analyzed. A novel time-efficiency number was introduced to evaluate the comprehensive performance of the time, energy conversion and efficiency of cold discharge. The results showed that the heat exchange balance during the cold charge and discharge stages had a thermal buffering effect on the storage unit. Forced convection caused by gas disturbance resulted in a larger cold discharge capacity and reduced the discharge time by a factor of 3 compared to operation without gas disturbance. In addition, the cold discharge capacity gradually increased with decreasing cold charge temperature and increasing flow rate. The cold discharge efficiency was more than 83% under different conditions. A comparison showed that the time-efficiency number tended to be larger with gas disturbance. This study showed that the time-efficiency number can be used for quantitative comparison of the cold discharge time and efficiency in hydrate cold storage systems.

Thermoelectricity and antivibration properties of screen-printed nanodoped In1.35ZnO2.11/In2O3 thin-film thermocouples on alumina substrates

Owing to the low flow field disturbances and fast response, thin-film thermocouples (TFTCs) are used to measure the service temperature of aero-engines. Indium tin oxide (ITO) and In2O3 are widely used in high–temperature measurements. However, ITO undergoes phase transition and consequent thermoelectric failure at above 1300 °C. In this study, In1.35ZnO2.11/In2O3 TFTCs were prepared on alumina substrates via screen printing method through introduction of ZnO nanopowder followed by annealing treatment. Results show that prepared TFTCs exhibited good thermoelectric properties at 1500 °C. The morphology, structure, and electrical coefficients of TFTCs were investigated. The average Seebeck coefficient was 39.8 μV/°C at 1500 °C with a drift rate (DT) of 0.84 °C/h, which was significantly improved with respect to that of ITO/In2O3, corresponding to 44.5 μV/°C at 1270 °C with a DT of 5.44 °C/h and failed at higher temperature. The result of lumped capacity method test show that the response time was 4.8 ms at 100 °C. Preliminary engine gas temperature measurements with a heat load of 1000 °C at 1 Mach show that these TFTCs are promising candidates for engineering applications. Finally, the structural reliability under high-magnitude vibration and impact tests (10–2000 Hz/20 g and 100 g/11 ms) was also investigated. As a result of the excellent bonding strengths of 47.36 and 59.83 N between the film and the substrate for both In1.35ZnO2.11 and In2O3, respectively, destructive cracking and peeling of the film were not observed, and no change in the Seebeck coefficient of the sample occurred after impact and vibration tests. These results provide an important basis for the potential application of In1.35ZnO2.11/In2O3 TFTCs in aero-engine high-temperature measurements of flow channel components.

Time-Sensitive Aspects of Mars Sample Return (MSR) Science.

Time-Sensitive Aspects of Mars Sample Return (MSR) Science.

Structural transformations in binary Ni62Nb38 alloy at ultrahigh temperatures

In this study, we performed the molecular dynamics simulation of the binary Ni62Nb38 alloy at heating from 300 K to 9000 K. The temperature dependences of the density and the fraction of liquid atoms were calculated. The boiling temperature of the system is determined. It has been established that near the temperature 7000 K the system undergoes phase transition from liquid to gas phase. It is shown that near the boiling temperature, the molten metal forms a branched structure. The obtained results made it possible to estimate the region of the liquid phase and to determine the probable scenario for the occurrence of structural changes near the boiling point.

Pulse laser precision truing of the V-shaped coarse-grained electroplating CBN grinding wheel

The machining difficulty has limited the further application of ultra-hard materials. For V-shaped coarse-grained electroplated cubic boron nitride (CBN) grinding wheel, a precise and efficient pulse laser truing method was proposed. Firstly, a theoretical model of the pulse laser truing process was established in order to optimize the laser truing energy distribution. Secondly, the effects of truing depth, grinding wheel speed, laser power and truing time were analyzed. Finally, the grinding performance of laser trued wheels were evaluated. The results showed that larger grinding wheel speed n would bring higher energy value and more stable energy distribution, truing depth h would not affect the value and stability of energy. CBN would not undergo phase transition and could bear more laser power Pavg. With the increase of truing time t, the geometric precision of V-shaped grinding wheel could be improved. The angle of V-shaped grinding wheel could reach 90.15° (deviation 0.02°), the bottom fillet radius was 53 μm (less than 100 μm). The surface roughness and grinding force corresponding to laser truing were less than that of mechanical truing, the truing time required was reduced by 72%∼83%, and the corresponding tooth profile angle and bottom fillet were basically the same.

Z-α1-antitrypsin polymers impose molecular filtration in the endoplasmic reticulum after undergoing phase transition to a solid state.

Misfolding of secretory proteins in the endoplasmic reticulum (ER) features in many human diseases. In α1-antitrypsin deficiency, the pathogenic Z variant aberrantly assembles into polymers in the hepatocyte ER, leading to cirrhosis. We show that α1-antitrypsin polymers undergo a liquid:solid phase transition, forming a protein matrix that retards mobility of ER proteins by size-dependent molecular filtration. The Z-α1-antitrypsin phase transition is promoted during ER stress by an ATF6-mediated unfolded protein response. Furthermore, the ER chaperone calreticulin promotes Z-α1-antitrypsin solidification and increases protein matrix stiffness. Single-particle tracking reveals that solidification initiates in cells with normal ER morphology, previously assumed to represent a healthy pool. We show that Z-α1-antitrypsin–induced hypersensitivity to ER stress can be explained by immobilization of ER chaperones within the polymer matrix. This previously unidentified mechanism of ER dysfunction provides a template for understanding a diverse group of related proteinopathies and identifies ER chaperones as potential therapeutic targets.

Discrete scale-invariant boson-fermion duality in one dimension

We introduce models of one-dimensional $n(\geq3)$-body problems that undergo phase transition from a continuous scale-invariant phase to a discrete scale-invariant phase. In this paper, we focus on identical spinless particles that interact only through two-body contacts. Without assuming any particular cluster-decomposition property, we first classify all possible scale-invariant two-body contact interactions that respect unitarity, permutation invariance, and translation invariance in one dimension. We then present a criterion for the breakdown of continuous scale invariance to discrete scale invariance. Under the assumption that the criterion is met, we solve the many-body Schr\"{o}dinger equation exactly; we obtain the exact $n$-body bound-state spectrum as well as the exact $n$-body S-matrix elements for arbitrary $n\geq3$, all of which enjoy discrete scale invariance or log-periodicity. Thanks to the boson-fermion duality, these results can be applied equally well to both bosons and fermions. Finally, we demonstrate how the criterion is met in the case of $n=3$; we determine the exact phase diagram for the scale-invariance breaking in the three-body problem of identical bosons and fermions. The zero-temperature transition from the unbroken phase to the broken phase is the Berezinskii-Kosterlitz-Thouless-like transition discussed in the literature.

Emulsions undergoing phase transition: Effect of emulsifier type and concentration

Pickering emulsion stabilized by cellulose nanocrystals (CNCs) during the phase transition of the dispersed oil is poorly understood. We investigated the capability of CNC in stabilizing Pickering emulsions during the temperature-induced phase transition. Paraffin wax emulsions stabilized by sodium dodecyl sulfate (SDS) were less stable than CNC stabilized emulsions. The relationship between droplet size and emulsifier content was examined, and a new model describing this relationship is proposed. The droplet size of CNC-based systems was not affected by temperature variation, even at low CNC concentrations. The minimum CNC content required to stabilize the paraffin wax emulsion was lower than SDS. DSC results indicated that higher droplet surface coverage with emulsifiers enhanced the deformation resistance of the crystallized droplets, which enhanced the emulsion stability. Temperature sweep viscosity measurements showed that the stability of CNC-based systems was not significantly impacted by the phase transition of the paraffin wax. Rheological amplitude sweep analysis indicated that emulsions above the melting point of paraffin wax were more stable at all strain levels. However, the SDS-based systems displayed substantial heterogeneity after the liquid-solid transition. Frequency sweep tests revealed that CNC-stabilized emulsions were more stable than SDS-stabilized emulsions.

Powder bed selective laser process (sintering/melting) applied to tailored calcium phosphate-based powders

This paper focuses on the tailoring of calcium phosphate powders for their use as powder bed selective laser process feedstock. Hydroxyapatite and chlorapatite were used as starting powders for the preparation of different blends through the addition of graphite as a laser absorptance additive. A methodical study was conducted to compare the processing windows of the blends containing different amounts of graphite through the laser patterning of circular samples. It was found that the addition of graphite increases the process window of the powder blends being the powder without additive non processable. Hydroxyapatite showed a clear phase transition (decreased when using higher volumetric energy density) into other calcium phosphate phases while chlorapatite was demonstrated to be thermally stable during the whole process (examined through X-ray diffraction and vibrational spectroscopies). In parallel, the study evaluating the powder blend composed of hydroxyapatite and graphite for the production of solid and complex parts was carried out although it required long printing times. The productivity of the process was improved by modification of printing parameters. Then, a series of solid samples were produced for the analysis of the microstructure and mechanical properties. High interconnected porosity was observed in the samples which could improve the bioactivity of the bioceramic scaffolds. A post-treatment of the parts increased their proportion in the hydroxyapatite phase and their mechanical properties. These results are expected to contribute to the application of powder bed selective laser processing of calcium phosphates powders toward bone tissue engineering. • Graphite as absorption additive improves the laser-material interaction enlarging the process window. • Laser parameters directly influence the hydroxyapatite phase transition into other calcium phosphate phases. • Chlorapatite did not undergo phase transition during the process due to its inherent higher thermal stability. • Solid parts containing a majority of HA phase in the structure were obtained although with low mechanical properties.

Calciolangbeinite-O, a natural orthorhombic modification of K2Ca2(SO4)3, and the langbeinite–calciolangbeinite solid-solution system

AbstractCalciolangbeinite, ideally K2Ca2(SO4)3, exists in two modifications, cubic and, first described in the present paper, orthorhombic. They are topologically-similar polymorphs which can be designated as calciolangbeinite-C and calciolangbeinite-O. Calciolangbeinite-O is the first natural orthorhombic langbeinite-like sulfate. It clearly differs from calciolangbeinite-C in the powder X-ray diffraction pattern, optical data and Raman spectrum. Calciolangbeinite-O is found in sublimates of the active Arsenatnaya fumarole at the Tolbachik volcano, Kamchatka, Far Eastern Region, Russia and in pyrometamorphic rocks of the Hatrurim Complex at Jabel Harmun, Judean Desert, Palestinian Autonomy and Har Parsa, Negev Desert, both in Israel. Calciolangbeinite-C is known only in fumarole sublimates at Tolbachik. Calciolangbeinite forms a continuous solid-solution system with langbeinite K2Mg2(SO4)3. The majority of the system is represented by cubic phases, and only members with compositions K2(Ca2.0–1.9Mg0.0–0.1)(SO4)3 have orthorhombic symmetry under room-temperature conditions. The crystal structure of calciolangbeinite-O was studied on a single crystal, chemically very close to K2Ca2(SO4)3, from Tolbachik (R1 = 2.75%). The unit-cell parameters are: a = 10.3330(2), b = 10.5027(2), c = 10.1763(2) Å, V = 1104.37(4) Å3 and Z = 4; space group is P212121. Calciolangbeinite-O is a low-temperature modification of K2Ca2(SO4)3 belonging to the K2Cd2(SO4)3 structure type whereas calciolangbeinite-C (space group P213), a high-temperature modification, has the langbeinite-type structure. The significant Mg admixture in calciolangbeinite-C from Tolbachik probably stabilises its cubic structure at room temperature. In both high-temperature fumaroles and pyrometamorphic rocks calciolangbeinite crystallises in the cubic modification, and during cooling its chemical variety close to the end-member K2Ca2(SO4)3 undergoes phase transition to calciolangbeinite-O, whereas the Mg-enriched varieties of the mineral remain calciolangbeinite-C.

Tuning Spin‐Orbit Torques Across the Phase Transition in VO2/NiFe Heterostructure

AbstractThe emergence of spin‐orbit torques as a promising approach to energy‐efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin‐orbit torques. Here, current‐induced spin‐orbit torques in VO2/NiFe heterostructures are investigated using spin‐torque ferromagnetic resonance, where the VO2 layer undergoes a prominent insulator‐metal transition. A roughly twofold increase in the Gilbert damping parameter, α, with temperature is attributed to the change in the VO2/NiFe interface spin absorption across the VO2 phase transition. More remarkably, a large modulation (±100%) and a sign change of the current‐induced spin‐orbit torque across the VO2 phase transition suggest two competing spin‐orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO2, corroborated by the first‐principles calculation of the spin Hall conductivity , is verified as the main source of the spin‐orbit torque in the metallic phase. The self‐induced/anomalous torque in NiFe, with opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO2, can be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin‐orbit torques of materials that undergo phase transitions for new device functionalities.

A thermodynamic model of phase transition of poly(N-isopropylacrylamide) hydrogels in ionic solutions

Submerged in an aqueous solution of sodium chloride (NaCl), a poly(N-isopropylacrylamide) (PNIPAM) hydrogel can be in one of two phases: swollen phase and collapsed phase. We measure the equilibrium volume of the hydrogel as a function of temperature T and ionic concentration y. The hydrogel is in the swollen phase when T and y are low, and is in the collapsed phase when T and y are high. We develop a thermodynamic model in which the free energy is a function of volume, temperature, and ionic concentration. The free energy also contains several adjustable parameters, which we best-fit to the experimental data of volume as a function of T and y. For a given pair of T and y, the free energy is a function of volume. This function has a single minimum for some pairs of (T, y), but two minima and a maximum for other pairs of (T, y). In the former, the single minimum corresponds to either a swollen or a collapsed state. In the latter, the lower minimum corresponds to a state of equilibrium, the higher minimum corresponds to a metastable state, and the maximum corresponds to an unstable state. When the two minima are equal, the hydrogel undergoes phase transition. The condition of phase transition is represented as a curve on the (T, y) plane. The thermodynamic model represents the experimental data well.

Precision Multi-Mode Dielectric Characterization of a Crystalline Perovskite Enables Determination of the Temperature-Dependent Phase Transitions.

Simple perovskite crystals undergo structural phase transitions on cooling to low temperatures, which significantly change the material properties of the crystal. In this work, we rigorously characterize the temperature evolution of permittivity of a perovskite crystal as it undergoes phase transitions. In particular, we have undertaken precision measurements of a single crystal of Strontium Titanate from 294.6 to 5.6 K, by measuring the frequency of multiple microwave transverse electric (TE) and magnetic resonant modes simultaneously. The multi-mode microwave measurement technique of resonant frequency used in this work allows high precision determination of any induced anisotropy of the permittivity as the crystal undergoes structural phase transitions. Compared with previous results, we unequivocally show that the permittivity has an isotropic value of 316.3±2.2 at room temperature, consistent with its well-known cubic structure, and determine the onset of dielectric anisotropy as the crystal is cooled to lower temperatures. We show that the crystal exhibits uniaxial anisotropy in the permittivity below 105 K when the structure becomes tetragonal, and exhibits biaxial anisotropy in the permittivity below 51 K when the structure becomes orthorhombic.

Crystal structure of nyerereite: A possible messenger from the deep Earth

Abstract Carbonates in the system Na2CO3-CaCO3 are nowadays suggested as having a wide stability field at conditions of the mantle transition zone. Our structural analysis of nyerereite, which has limited stability fields at ambient conditions, and its similarities with already known carbonates that are stable at high-pressure conditions, allowed us to propose that nyerereite likely undergoes phase transitions at both high-pressure and high-temperature conditions. This supports the hypothesis that nyerereite takes part in carbon transportation from the mantle/deep crust toward the surface, with important implications for the deep carbon cycle associated with carbonatites. K-free nyerereite [Na2Ca(CO3)2] was synthesized both at hydrothermal conditions and from the melt. The structure of nyerereite was refined as a three-component twinned structure in the centrosymmetric Pbca space group with ratios of the three twinning components 0.221(3):0.287(3):0.492(3). Twinning at micro- and nano-level can introduce some minor structural deformations that influence the likely occurrence of the inversion center as one of the symmetry elements in the nyerereite structure. Based on the automated topological algorithms, we show that nyerereite has a unique crystal structure, not having analogs among the known structures, except for the structure with a similar composition K2Ca(CO3)2 fairchildite. A comparison between the centrosymmetric Pbca nyerereite structure and that of aragonite (CaCO3, Pmcn space group) reveals two main scenarios for the high-pressure form of Na2Ca(CO3)2: (1) poly-somatic relations as the interlayering of the high-pressure polymorph Na2CO3 and CaCO3-aragonite, and (2) high-pressure structure with ninefold-coordinated Na and Ca sites resembling that of aragonite. Our discussion heightens the interest in the high-pressure behavior of the nyerereite structure and strengthens the hypothesis about the possibility for nyerereite to be stable at high-pressure/high-temperature conditions.

A Quantum Space Model of Cosmic Evolution: Dark Energy and the Cyclic Universe

We present a Quantum Space Model (QSM) of cosmic evolution based on the theory that space consists of energy quanta from which our universe came about. We used the Friedmann equations to trace its history and predict its ultimate fate. Results provide further support to our recent proposal that the accelerating expansion of the universe is due to a scalar space field which has become known as Dark Energy. In our model, the universe started from high energy space quanta which were triggered by quantum fluctuations that caused the Big Bang. It then expanded and cooled undergoing phase transitions to radiation, fundamental particles, and matter. Matter agglomerated and grew into stars, galaxies, etc. and was eventually consolidated by gravity into Black Holes, which finally ended in a Big Crunch in a state of deep freeze inside the Black hole at 1.380 trillion years. Fluctuations, quantum tunneling, or some other mechanisms caused a new Bang to start another cycle in its life. Our results are in good agreement with the theoretical predictions of a cyclic universe by Steinhardt and his associates, and by Penrose. Space and energy are equivalent as embodied in the Planck energy equation. They give rise to the two principal long range forces in the universe: the gravitational force and the space force. The latter may be the fifth force in the universe. The two forces could provide the clockwork mechanism operating our cyclic universe. If the Law of Conservation of Energy is universal, then the cosmos is eternal.

Exploration-exploitation in multi-agent learning: Catastrophe theory meets game theory

Exploration-exploitation is a powerful and practical tool in multi-agent learning (MAL); however, its effects are far from understood. To make progress in this direction, we study a smooth analogue of Q-learning. We start by showing that our learning model has strong theoretical justification as an optimal model for studying exploration-exploitation. Specifically, we prove (1) that smooth Q-learning has bounded regret in arbitrary games for a cost model that explicitly balances game-rewards and exploration-costs, i.e., costs from testing potentially suboptimal actions, and (2) that it always converges to the set of quantal-response equilibria (QRE), the standard solution concept for games with bounded rationality, in arbitrary weighted potential games. In our main task, we then turn to measure the effect of exploration on collective system performance. We characterize the geometry of the QRE surface in low-dimensional MAL systems and link our findings with catastrophe (bifurcation) theory. In particular, as the exploration hyperparameter evolves over-time, the system undergoes phase transitions where the number and stability of equilibria can change radically given an infinitesimal change to the exploration parameter. Based on this, we provide a formal theoretical treatment of how tuning the exploration parameter can provably lead to equilibrium selection with both positive as well as negative (and potentially unbounded) effects to system performance.