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We show that dislocations in active two-dimensional (2D) smectic liquid crystals with underlying rotational symmetry are always unbound in the presence of noise, meaning the active smectic phase does not exist for nonzero noise in d=2. The active smectic phase can, like equilibrium smectics in 2D, be stabilized by applying rotational symmetry-breaking fields; however, even in the presence of such fields, active smectics are still much less stable against noise than equilibrium ones, when the symmetry-breaking field(s) are weak.

Although human beings have known about the phenomenon of “flocking”- that is, the coherent movement of large numbers of creatures (flocks of birds, schools of fish, herds of woolly mammoths, etc.)- since prehistoric times, it is only in the last two decades that we have begun to truly understand this phenomenon. In particular, the surprising fact that a very large collection of organisms in two dimensions cannot all point in the same direction, but can quite easily move in the same direction, can now be explained. In these lectures, I’ll review one of the principal theoretical tools that made this possible: hydrodynamics. My intention is both to elucidate flocking- or, to use the specific technical mouthful, “polar ordered dry active fluids”-, and to use flocking as an illustration of how to use the hydrodynamic approach on new and unfamiliar systems.

We present a hydrodynamic theory of incompressible polar active fluids with quenched random field disorder. This theory shows that such fluids can overcome the disruption caused by the quenched disorder and move coherently, in the sense of having a nonzero mean velocity in the hydrodynamic limit. However, the scaling behavior of this class of active systems cannot be described by linearized hydrodynamics in spatial dimensions between 2 and 5. Nonetheless, we obtain the exact dimension-dependent scaling exponents in these dimensions.

We show that incompressible polar active fluids can exhibit an ordered, coherently moving phase even in the presence of quenched disorder in two dimensions. Unlike such active fluids with annealed (i.e., time-dependent) disorder only, which behave like equilibrium ferromagnets with long-range interactions, this robustness against quenched disorder is a fundamentally non-equilibrium phenomenon. The ordered state belongs to a new universality class, whose scaling laws we calculate using three different renormalization group schemes, which all give scaling exponents within 0.02 of each other, indicating that our results are quite accurate. Our predictions can be quantitatively tested in readily available artificial active systems, and imply that biological systems such as cell layers can move coherently in vivo, where disorder is inevitable., 6 pages

We study the moving phase of two-dimensional (2D) incompressible polar active fluids in the presence of both quenched and annealed disorder. We show that long-range polar order persists even in this defect-ridden two-dimensional system. We obtain the large-distance, long-time scaling laws of the velocity fluctuations using three distinct dynamic renormalization group schemes. These are an uncontrolled one-loop calculation in exactly two dimensions, and two $d=(d_c-\epsilon)$-expansions to $O(\epsilon)$, obtained by two different analytic continuations of our 2D model to higher spatial dimensions: a ``hard" continuation which has $d_c={7\over 3}$, and a ``soft" continuation with $d_c={5\over 2}$. Surprisingly, the quenched and annealed parts of the velocity correlation function have the same anisotropy exponent and the relaxational and propagating parts of the dispersion relation have the same dynamic exponent in the nonlinear theory even though they are distinct in the linearized theory. This is due to anomalous hydrodynamics. Furthermore, all three renormalization schemes yield very similar values for the universal exponents, and, therefore, we expect the numerical values we predict for them to be highly accurate., Comment: 39 pages, 11 figures

In recent years, the role of self-tracking technologies has been investigated, debated and critiqued within qualitative research circles. The principal means by which self-tracking technologies seek to promote health-related behaviours and behaviour change is through the use of ‘nudges’. Despite the increasing prevalence of nudge-style modes of body-mind governance, there remains little in-depth qualitative research on people’s embodied responses to this form of behavioural management. The current study sought to address this lacuna by drawing on a form of empirical, sociological phenomenology to investigate the lived experience of being ‘nudged’ by self-tracking technology. Our phenomenologically-inspired analysis revealed how nudges can be perceived as objectifying by rendering the user’s body the intentional object of awareness. Participants agentically engaged in a sense-making process, actively (re)interpreting the relevance of nudges and assessing critically the prescribed action in the context of their everyday life. Users expressed confidence in their own embodied sensory perceptions and assessment, and resisted having their bodily intuition displaced by ‘unbodied’ data.

The aim of this study was to examine the effect of bio-banding on technical and tactical markers of talent identification in 11- to 14-year-old academy soccer players.Using a repeated measures design, 92 players were bio-banded using percentage of estimated adult stature attainment (week 1), maturity-offset (week 2) and a mixed-maturity method (week 3). All players contested five maturity (mis)matched small-sided games with technical and tactical variables measured. Data were analysed using a series of Bayesian hierarchical models, fitted with different response distributions and different random and fixed effect structures.Despite differences during maturity-matched bio-banding for post-peak height velocity players, very few tactical differences were evident during the remaining maturity-matched and mis-matched fixtures for both banding methods. In fact, the results showed no consistent differences across both banding methods for practitioner and video analysis-derived technical performance characteristics during maturity matched and mis-matched fixtures. Both bio-banding methods explained similar levels of variance across the measured variables.Maturity-matched bio-banding had some effect on both technical and tactical characteristics of players during maturity-matched bio-banded formats. That said, this trend remained during maturity mis-matched bio-banded formats which restricts the conclusions that can be made regarding the effectiveness of bio-banding to manipulate technical and tactical measures in academy soccer players.

Traditional models of skill learning posit that skilled action unfolds in an automatic manner and that control will prove deleterious to movement and performance proficiency. These perspectives assume that automated processes are characterised by low levels of control and vice versa. By contrast, a number of authors have recently put forward hybrid theories of skilled action which have sought to capture the close integration between fine-grained automatic motor routines and intentional states. Drawing heavily on the work of Bebko et al. (2005) and Christensen et al. (2016), we argue that controlled and automated processes must operate in parallel if skilled performers are to address the wide range of challenges that they are faced with in training and competition. More specifically, we show how skilled performers use controlled processes to update and improve motor execution in training contexts and to stabilise performance under pressurised conditions.

I show that non-equilibrium two-dimensional interfaces between three dimensional phase separated fluids exhibit a peculiar "sub-logarithmic" roughness. Specifically, an interface of lateral extent $L$ will fluctuate vertically (i.e., normal to the mean surface orientation) a typical RMS distance $w\equiv\sqrt{\langle |h(\br,t)|^2\rangle} \propto [\ln{(L/a)}]^{1/3}$ (where $a$ is a microscopic length, and $ h(\br,t)$ is the height of the interface at two dimensional position $\br$ at time $t$). In contrast, the roughness of equilibrium two-dimensional interfaces between three dimensional fluids, obeys $w \propto [\ln{(L/a)}]^{1/2}$. The exponent $1/3$ for the active case is exact. In addition, the characteristic time scales $\tau(L)$ in the active case scale according to $\tau(L)\propto L^3 [\ln{(L/a)}]^{1/3}$, in contrast to the simple $\tau(L)\propto L^3$ scaling found in equilibrium systems with conserved densities and no fluid flow., Comment: 4 pages, no figures

We consider the effect of spatial anisotropy on polar flocks by investigating active $q$-state clock models in two dimensions. In contrast to what happens in equilibrium, we find that, in the large-size limit, any amount of anisotropy changes drastically the phenomenology of the rotationally-invariant case, destroying long-range correlations, pinning the direction of global order, and transforming the traveling bands of the coexistence phase into a single moving domain. All this happens beyond a lengthscale that diverges in the $q\to\infty$ limit. A phenomenology akin to that of the Vicsek model can thus be observed in a finite system for large enough values of $q$. We provide a scaling argument which rationalizes why anisotropy has so different effects in the passive and active cases., Comment: 6 pages with 4 figures. 4 pages of supplementary information (as ancillary file)

This chapter considers whether optimal/peak performance is as automatic or ‘mindless’ as many accounts of expertise suggest. It starts by exploring the phenomenon known as ‘flow’ which is typically presented as evidence that peak performance is mindless or automatic in nature. It then reviews recent literature in this area which reveals that the mind remains online during skilled action and especially during ‘clutch’ performances or when athletes are seeking to ‘make it happen’. It proceeds to discuss how ‘mindedness’ and bodily awareness are integral features of peak performance. It then uses this argument to uncover the potential perils associated with ‘non-mindedness’ or automated performance. In particular, the chapter discusses how excessive automaticity prevents athletes from exercising attentional control and results in a number of undesirable outcomes including slips, lapses, and in extreme cases, ‘choking’ under pressure.

What is the role of habitual movement in expert action? This chapter begins by reviewing traditional conceptualizations of habit according to which our well-learned movements are mechanical-like tendencies to respond to stimuli in a preordained manner. It then draws on a range of theoretical perspectives which emphasize the generative nature of habits. It proceeds to discuss a variety of the ‘crises’ which confront the performing body (e.g. injury, ageing, normalization of bodily processes) and suggest that habits must be inherently flexible if experts are to successfully address these latter challenges. In doing so, it draws on the work of theorists such as Bourdieu, Carlisle, and Dewey. The chapter concludes by discussing some of the pedagogical strategies such as discursive practice that coaches and practitioners may use to extend habitual movement capacities and address habitual crises. It argues that experts acquire flexible habits which allows them to act back upon the body and to initiate change.

A considerable volume of research has explored spectators’ attraction to the aesthetic aspects of sport. However, considerably less attention has been devoted to an evaluation of the aesthetic dimension of sport from the performer’s perspective. This chapter hypothesizes that such evaluation can benefit athletic skill. It substantiates and elucidates some of the types of aesthetic experiences athletes may undergo and considers their potential use in sports. The chapter argues that athletes sometimes evaluate their actions by determining whether they have certain aesthetic quality, such as whether a movement embodies power or feels somehow just beautifully right. In bringing some of these ideas together it considers how an athlete’s aesthetic awareness of their own movements might be conducive to better practice and performance. This thesis is propaedeutic to future empirical work investigating the role of aesthetic self-evaluation in athletic performance.

What role might intuition and deliberation play during the performance of well-learned skills? Dreyfus and Dreyfus’ (1986) influential phenomenological analysis of skill-acquisition proposes that expert performance is guided by non-cognitive responses which are fast, effortless, and intuitive in nature. Although Dreyfus and Dreyfus (1986) recognize that, on occasions (e.g. when performance goes awry for some reason), a form of ‘detached deliberative rationality’ may be used by experts to improve their performance, they see no role for calculative problem solving or deliberation (i.e. drawing on rules or mental representations) when performance is going well. The current chapter counters this argument by drawing on empirical evidence and phenomenological description to argue that skilled performers use cognitive control (an executive function) across a range of sporting situations (i.e. in training, pre-performance routines, on-line skill execution) in order to maintain and enhance performance proficiency.

This penultimate chapter considers how athletes might develop the ability to exert attentional control. It outlines some approaches that might help athletes to switch their focus or re-distribute patterns of attention when they realize they have adopted task-irrelevant thoughts. It evaluates the use of mindfulness, quiet-eye training, pressurized training, among other approaches, as means of training attentional control. The chapter concludes by outlining a series of methodological approaches that might be employed by researchers wishing to test some of the predictions put forth by our model of skilled action and our proposal that skilled maintenance is underpinned by the flexible deployment of attentional resources.

After identifying some of the weaknesses associated with linear, or serial, models of skill learning—with a focus on their failure to fully account for the ongoing relevance of motor control and attention to action—this chapter synthesizes the evidence presented over the course of this book to construct a model of skilled action that captures the complex relationship between automaticity and attentional focus. This model explains how these two processes operate in a synergistic fashion to help experts overcome the challenges they face in seeking to not only maintain but to continue to improve performance proficiency over long timescales, to update and improve motor execution in training contexts, and to stabilize performance under pressurized conditions. The chapter concludes by briefly discussing the role metacognition plays in allowing expert performers to identify and apply situationally appropriate modes of control.

In this chapter, the phenomenon of continuous improvement is introduced and it is suggested that conscious processes play a crucial role in the maintenance and improvement of performance proficiency among skilled performers. This thesis is intriguing because it runs counter to a body of research warning us of the perils of thinking too much, or even at all, about highly practised movement. By contrast, it argues that continuous improvement is mediated by a performer’s ability to reflect and consciously guide their action during practice and performance. It critically evaluates some of the dominant paradigms in the skill acquisition literature, including information processing approaches and theories of embodiment, and explains why the book’s stance is intellectualist and pragmatic in nature. Lastly, it provides an overview of the remaining chapters in the book.

Prominent theories of skill acquisition posit that the performing body is absent during ‘habitualized’ or well-learned action. This chapter challenges this position by arguing that the body is never forgotten during skilled movement. Instead, it possesses what might be termed an enduring presence. Drawing on Colombetti’s (2011) taxonomy of the bodily self, the chapter shows how skilled performers may experience either a reflective or pre-reflective mode of bodily awareness depending on what they attend to during online skill execution. It proposes that while the body is always lived through as the subject of experience, performers will often have little choice but to take the body as the intentional object of their awareness. The chapter concludes by arguing that it is the dynamic interplay of various forms of bodily awareness that facilitates optimal performance and allows skilled performers to confront the challenges (e.g. injury, performance slumps) that are a ubiquitous feature of competitive environments.

The final chapter synthesizes the arguments presented over the course of the book by suggesting that skill execution continues to be governed by conscious processes even after performers have attained a high level of expertise. It argues that skill-focused attention is necessary if experts are to eschew proceduralization and react flexibly to ‘crises’ and fine-grained changes in situational demands. In doing so, it discusses the role played by conscious control, reflection, and bodily awareness in maintaining performance proficiency. It suggests that skill maintenance and continuous improvement are underpinned by the use of both automated procedures (acknowledging that these are inherently active and flexible) and metacognitive knowledge. The chapter concludes by briefly considering how skill-focused attention needs to be applied in both training and performance contexts in order to facilitate continuous improvement.

How do great athletes defy the power law of practice, according to which improvements in skill eventually plateau? To solve this puzzle, this book presents a theory of ‘continuous improvement’ which emphasizes the role that conscious processes play in maintaining and advancing skilled performers’ movement capacities. It argues that continuous improvement requires the use of processes such as abstract thought and bodily awareness in order to strategically alter and improve habitual movements in response to contextual demands. The book also elucidates a number of strategies that might be used to improve an athlete’s attentional control and help them switch their focus when they realize they have adopted task-irrelevant thoughts. Finally, it presents a range of methodological approaches that might be used by researchers to better understand the attentional flexibility that characterizes skilled action across training and performance contexts.

Blowing the whistle on corruption or wrongdoing can facilitate the detection, investigation, and then prosecution of a violation that may have otherwise gone undetected. The purpose of this systematic review was to identify the factors that are associated with intentions to blow the whistle on wrongdoing. We searched Academic Search Premier, CINAHL Complete, Education Research Complete, ERIC, Medline, PsycARTICLES, PsycINFO, Regional Business News, and SPORTDiscus in January 2020. The quality of evidence was assessed using the Cochrane risk of bias tool. Of the 9,136 records identified, 217 studies were included in this systematic review. We identified 8 dimensions, 26 higher-order themes, and 119 lower-order themes. The whistleblowing dimensions were personal factors, organizational factors, cost and benefits, outcome expectancies, the offense, reporting, the wrongdoer, and social factors. Based on the findings, it is apparent that organizations should empower, educate, protect, support, and reward those who blow the whistle, in order to increase the likelihood on individuals blowing the whistle on corruption and wrongdoing. A combined approach may increase whistleblowing intentions, although research is required to test this assertion. From a policy perspective, more consistent protection is required across different countries.

Objectives The present paper elucidates some cognitive mechanisms of expertise in sport that have emerged from recent studies of three topics in psychology: motor imagery; flow and “clutch” states; and the “quiet eye” phenomenon. Design A selective narrative review was conducted of research on the three preceding topics. Special consideration was given to recent studies by European researchers on these topics. Method Following a brief overview of theoretical approaches to sport expertise, the paper examines certain cognitive mechanisms of elite athletic performance that have emerged from recent studies of motor imagery; flow and “clutch” states; and the “quiet eye” phenomenon. In the final section, conclusions are drawn about theoretical progress in understanding the cognitive mechanisms of expertise in sport. Results The mechanisms underlying sport expertise reflect both task-specific and universal cognitive processes (e.g., mental representations). Conclusion Considerable progress has been made in identifying the cognitive mechanisms underlying expertise in sport but additional research is required to address certain unresolved issues in this field.

We present the hydrodynamic theory of coherent collective motion ("flocking") at a solid-liquid interface, and many of its predictions for experiment. We find that such systems are stable, and have long-range orientational order, over a wide range of parameters. When stable, these systems exhibit "giant number fluctuations", which grow as the 3/4th power of the mean number. Stable systems also exhibit anomalous rapid diffusion of tagged particles suspended in the passive fluid along any directions in a plane parallel to the solid-liquid interface, whereas the diffusivity along the direction perpendicular to the plane is not anomalous. In the remaining parameter space, the system becomes unstable., 6 pages, 2 figs

We construct the hydrodynamic theory of coherent collective motion ("flocking") at a solid-liquid interface. The polar order parameter and concentration of a collection of "active" (self-propelled) particles at a planar interface between a passive, isotropic bulk fluid and a solid surface are dynamically coupled to the bulk fluid. We find that such systems are stable, and have long-range orientational order, over a wide range of parameters. When stable, these systems exhibit "giant number fluctuations", i.e., large fluctuations of the number of active particles in a fixed large area. Specifically, these number fluctuations grow as the $3/4$th power of the mean number within the area. Stable systems also exhibit anomalously rapid diffusion of tagged particles suspended in the passive fluid along any directions in a plane parallel to the solid-liquid interface, whereas the diffusivity along the direction perpendicular to the plane is non-anomalous. In other parameter regimes, the system becomes unstable., Comment: 52 pages, 3 figures

The aim of this study was to examine the effect of bio-banding on indicators of talent identification in academy soccer players. Seventy-two 11 to 14-year-old soccer players were bio-banded using percentage of estimated adult stature attainment (week 1), maturity-offset (week 2) or a mixed-maturity method (week 3). Players contested five maturity (mis)matched small-sided games with physical and psychological determinants measured. Data were analysed using a series of Bayesian hierarchical models, fitted with different response distributions and different random and fixed effect structures. Few between-maturity differences existed for physical measures. Pre-peak height velocity (PHV) and post-PHV players differed in PlayerLoadTM (anterior-posterior and medial-lateral) having effect sizes above our criterion value. Estimated adult stature attainment explained more of the variance in eight of the physical variables and showed the greatest individual differences between maturity groups across all psychological variables. Pre-PHV and post-PHV players differed in positive attitude, confidence, competitiveness, total psychological score (effect sizes = 0.43-0.69), and session rating of perceived exertion. The maturity-offset method outperformed the estimated adult stature attainment method in all psychological variables. Maturity-matched bio-banding had limited effect on physical variables across all players while enhancing a number of psychological variables considered key for talent identification in pre-PHV players.

We show that "Malthusian flocks" -- i.e., coherently moving collections of self-propelled entities (such as living creatures) which are being "born" and "dying" during their motion -- belong to a new universality class in spatial dimensions $d>2$. We calculate the universal exponents and scaling laws of this new universality class to $O(\epsilon)$ in an $\epsilon=4-d$ expansion, and find these are different from the "canonical" exponents previously conjectured to hold for "immortal" flocks (i.e., those without birth and death) and shown to hold for incompressible flocks in $d>2$. Our expansion should be quite accurate in $d=3$, allowing precise quantitative comparisons between our theory, simulations, and experiments., Comment: 5 pges, 2 figures. This new version has essentially the same content as the earlier one, but differs cosmetically, and is the version actually submitted to PRL. The accompanying long paper is titled "A novel nonequilibrium state of matter: a $d=4-\epsilon$ expansion study of Malthusian flocks"

We show that "Malthusian flocks"-i.e., coherently moving collections of self-propelled entities (such as living creatures) which are being "born" and "dying" during their motion-belong to a new universality class in spatial dimensions d>2. We calculate the universal exponents and scaling laws of this new universality class to O(e) in a d=4-e expansion and find these are different from the "canonical" exponents previously conjectured to hold for "immortal" flocks (i.e., those without birth and death) and shown to hold for incompressible flocks with spatial dimensions in the range of 2

This chapter focuses on fundamental influences of motoric factors during execution; provides evidence to support the desirability and applicability of conscious motor processing under pressure conditions; and suggests some empirically informed guidelines for what couldbe considered good practice. Athletes are often required to execute motor skills under conditions of competitive pressure. Consequently, achieving and maintaining high levels of performance under dynamic, stressful, and demanding situations is an essential characteristic of successful performance. At the top-flight of any sport, the consequences and meaningfulness of performance are often great, especially when the stakes are at their highest. Optimal/automatic is essentially a state in which peak performance is reached in an effortless manner; actions are consistent, smooth, and effortless with minimal/supervisory conscious control during execution. Reflecting non-observable changes to execution processes that underpin performance gains, data show a restructuring of cognitive architecture with skill improvements.

We study the dynamics of a contractile active nematic fluid subjected to a Poiseuille flow. In a quasi-1D geometry, we find that the linear rheology of this material is reminiscent of Darcy's law in complex fluids, with a pluglike flow decaying to zero over a well-defined ``permeation'' length. As a result, the viscosity increases with size, but never diverges, thereby evading the yield stress predicted by previous theories. We find strong shear thinning controlled by an active Ericksen number quantifying the ratio between external pressure difference and internal active stresses. In 2D, the increase of linear regime viscosity with size only persists up to a critical length beyond which we observe active turbulent patterns, with very low apparent viscosity. The ratio between the critical and permeation length determining the stability of the Darcy regime can be made indefinitely large by varying the flow aligning parameter or magnitude of nematic order.

We show that "Malthusian flocks"-i.e., coherently moving collections of self-propelled entities (such as living creatures) which are being "born" and "dying" during their motion-belong to a new universality class in spatial dimensions d2. We calculate the universal exponents and scaling laws of this new universality class to O(ε) in a d=4-ε expansion and find these are different from the "canonical" exponents previously conjectured to hold for "immortal" flocks (i.e., those without birth and death) and shown to hold for incompressible flocks with spatial dimensions in the range of 2d≤4. We also obtain a universal amplitude ratio relating the damping of transverse and longitudinal velocity and density fluctuations in these systems. Furthermore, we find a universal separatrix in real space (r) between two regions in which the equal-time density correlation 〈δρ(r,t)δρ(0,t)〉 has opposite signs. Our expansion should be quite accurate in d=3, allowing precise quantitative comparisons between our theory, simulations, and experiments.

The present study investigated the prevalence and influence of psychosocial factors amongst a sample of highly-skilled athletes who had previously attempted to refine their technique. Semi-structured qualitative interviews were conducted with eight tennis players to gain an in-depth understanding of their experiences during the process. Results revealed that participants sought to refine their technique in order to address an “attenuated” movement pattern perceived as causing a competitive disadvantage. Addressing the psychosocial factors of interest here, commitment and confidence were reportedly important concomitants during the refinement process. Upon reflection, participants indicated that taking a break from competition and dedicating more time to the refinement might have increased the likelihood of effective change and performance improvement. Overall, findings indicate that psychosocial factors have a significant influence on players’ ability to successfully enact technical refinement. However, it is suggested that greater consideration towards other motoric factors could also have improved levels of success. In conclusion, while the importance for change was understood, there is a need for improved understanding and planning in terms of how a coach might operationalise these factors within training for the competition environment.

Fitness trackers or ‘wearables’ are being used by an ever-increasing number of exercisers to self-monitor their health, wellbeing and fitness. While acknowledging that many users find self-tracking devices to be an important part of their exercise regime, the current paper draws on phenomenological and empirical evidence to argue that the use of fitness trackers for the purposes of “bio-monitoring” may have a number of undesirable consequences. I argue that the prolonged use of these devices may, in some cases, normalize/objectify the embodied subject and contribute to an anesthetisation of human experience. This arises as neo-liberal projects encourage “self-trackers” to consider their bodily functioning in quantifiable terms thereby reducing the attention that one may pay to the embodied sensations that accompany physical activity. I suggest that this is likely to hinder one’s enjoyment of exercise and prevent users from generating the flexible and adaptive habits that are necessary to expand one’s productive capacities in the world. I conclude by briefly considering how wearable devices may be used in a manner which counteracts the surveillance or regulatory intentions of bio-monitoring technologies and allows users to repurpose these technologies in ways which work for them.

Theorists have used the concept of habitus to explain how skilled agents are capable of responding in an infinite number of ways to the infinite number of possible situations that they encounter in...

The effect of quenched (frozen) disorder on the collective motion of active particles is analyzed. We find that active polar systems are far more robust against quenched disorder than equilibrium ferromagnets. Long ranged order (a non-zero average velocity $\langle{\bf v}\rangle$) persists in the presence of quenched disorder even in spatial dimensions $d=3$; in $d=2$, quasi-long-ranged order (i.e., spatial velocity correlations that decay as a power law with distance) occurs. In equilibrium systems, only quasi-long-ranged order in $d=3$ and short ranged order in $d=2$ are possible. Our theoretical predictions for two dimensions are borne out by simulations., 5 pages, 1 figure. The short paper on flocking with quenched noise