Plasmodium Falciparum Essay Example | Topics and Well Written Essays - 750 words

Plasmodium Falciparum - Essay Example The last is becomes infected in this way. All stages of malarial plasmodium development taking place in the body of the carrier – in a human, a bird and a mosquito. Such Sporozoa sporozoites are developed in the body of the mosquito and further transmitted to birds or human with saliva from the mosquito`s bite. Life cycle and transmission. The life cycle of Plasmodium falciparum is associated with changes of hosts. One part of the life cycle takes place in the human body where the parasites reproduce asexually; the second part occurs in the body of a specific carrier of malaria – female mosquito Anopheles, where plasmodium reproduces sexually (Dantzler et al.). Therefore, for Plasmodium falciparum, the human is an intermediate carrier, and the female Anopheles mosquito is the final host. Infection by Plasmodium falciparum occurs during sucking blood of patients with malaria and then mosquito infects another person by introducing parasites with its saliva during the bite. Via infected mosquito`s saliva the sporozoites enter the bloodstream of host and within 30-40 min get into a place of primary localization – into the liver cells (Dantzler et al.). There takes place an intracellular parasite asexual reproduction called tissue (exoerythrocytic) schizogony. From each of spo rozoites, a several thousand merozoites are formed. Further, they destroy hepatocytes and released into the bloodstream. The duration of this period is about 6-9 days. Merozoites penetrate into erythrocytes and thus begin the blood stage with trophosoite formation and erythrocytic schizogony (Wright and Rayner). In erythrocytes cells, the trophozoite is consistent passes through the ring, amoebic, mature trophozoite, schizont and merozoite stages. During schizogony, in erythrocytes occurs the formation of schizonts. Further, each schizont gives a rise to the several dozen of small merozoites

How employees react when facing organization change and what HR Literature review

How employees react when facing organization change and what HR manager should do - Literature review Example None of the mini computer companies could succeed in the business of personal computers Business schools and medical colleges are finding a hard tome to transform their curriculum according to the types of doctors and managers that are in demand in the market (Christensen & Overdorf, 2000, p.67). There are numerous other examples displaying the same challenge. It is seen that change efforts fail primarily because employers fail to handle the resistance towards change from employees. Managing change successfully means managing the fear of people. However, the peoples’ reactions to change efforts remain irrational and unsuccessful. Resistance towards the change originates from the fear of the unknown and apprehensions about a loss. HR managers play the crucial role of managing the reaction or response of employees towards the change process. The apparent reason to peoples’ fears is the way they perceive the change process, while the back end reaction to the change process is the extent to which they are equipped to deal with the change process. ... The project brings forth numerous critical reviews and suggestions of researchers and practitioners on the subject and delivers a critical analysis. It also puts forth their views regarding how changes can be managed effectively through effective people management procedures (Adair, 2007, p.124). Literature Review- How employees react when facing organization change and what HR manager should do Employee Resistance to Change- Critical Analysis The research begins with analysis of the greatest challenges of managing change initiatives in the organization. Managing organizational change is a difficult process as the conditions under which it is undertaken at the initial stage keeps changing. As situations keep shifting it becomes increasingly difficult for the top managers and agents to prepare for manage the change process in a way which satisfied both employers and employees. It is not surprising to understand that change resistance has attracted immense attention from practitioners and researchers. Immense attention has gone into the understanding of determinants and sources of change resistance. The general public and the media have gone into various forms of active resistances such as protests and strikes. Some of the other forms of organizational resistances are passive resistance, which is comparatively less observable, but has immensely attracted the concern of employers in organizations. Unsurprisingly, resistance towards change initiatives account for being one of the most crucial sources of organizational change failures (Conger & Kanungo, 1998, p.8). Meyer, (1982) and Nadler, (1998) have defined the concept of organizational change as the effort or the series of efforts which is designed in a manner to bring about change or transformation in

Implementation of a Palmprint Recognition System

Implementation of a Palmprint Recognition System CHAPTER -VI 6. CONCLUSION SCOPE OF FUTURE WORK There are some key aspects to discuss about this thesis in general. First, it is important to mention that the main objective of this work implementation of a palmprint recognition system was successfully accomplished. Biometrics plays an important role in personal identification. The importance of biometrics in everyday life has been discussed and different biometric technologies are introduced. It has been shown that palm can also be a good biometric. The work reported in this thesis is summarized in this chapter. This Research Work proposed a novel approach for Palmprint Biometric Authentication System to identify the individuals based on their palmprints. The approach novelty could be found in the combinations between palmprints images transform techniques, features reduction technique and feed-forward neural network classifier. CASIA pre-processed hyperspectral database and MATLAB version 2016a with supporting toolboxes were used in our experiment work. Firstly, each pre-proce ssed palmprint image has read by MATLAB internal function, and it has transformed by using multiscale toolboxes in order to convert each image into data. The resulted data is projected by dimensionality reduction tool. Finally, neural network toolbox used for recognition training and verification the resulted vectors. We manually prepare proposed Gabor Wavelet and Local Binary Pattern function along with all Other function in MATLAB 2016 and a database of 200 palm images of 20 people is considered for the validation. This Thesis Work considers a novel and efficient method for the palmprint identification based on Gabor wavelet by using multi-block local binary patterns. Proposed method is further supervised through our proposed multi-layer feed-forward neural network for more accurate and computationally efficient recognition. Gabor wavelets efficiently filter the pre-processed image for getting optimum texture features through MB-LBP. Due to accurate feature representation of palm images through proposed LBP, anticipated MLFFNN training rate is high and we are getting much accurate results comparatively. Experiments are performed to make an analysis for the optimal palm region and LBP neighbourhood. We investigate the matching accuracy for the optimal parameters. The performance of the proposed method in term of accuracy and some other parameters is obtained and compared with some recent methods. These local characteristics are summed and orientation corresponding maximum local intensity pattern is conceded as optimal local direction. Micro pattern representation is obtained by LBP descriptor. Feature vector is prepared by histograms of 256 bins. In our proposed scheme we use the Gabor wavelets, which has wavelet like property, in orthogonal direction and smoothest contours. Orientation extraction is done optimally to get directional representation and feature size is reduced by extracting LBP histograms. Accuracy of Proposed system is about 99.6% and error rate is below 0.9%. Compared to other existing method proposed method provides robustness to noise, low complexity and small features length. Secondly 3x 3 direction pattern employed which extract the edge characteristics locally. Direction pattern further emphasis edge orientation and filter out non edges along irrespective direction of pattern. Local aggregation gives higher value (Local Intensity) at particular orientation. So, the competition for maximum local intensity can better select the orientation information. Secondly orientation information is not affected by intensity variations. Because of these reasons, it is obvious that our method is performing well. In this palm print recognition system, features such as region mask, orientation field and minutiae are being extracted. An efficient matching algorithm is being implemented which uses these features for comparison of the query palm print with the database. Hence this system tests the image with the database and checks if the person is aut henticated or not. This authentication system can be used in forensic science and other border control systems for authentication of palm prints. the proposed work is also tested on colour RGB (multi-dimensional) images and real time palm images. Further Works For future work, the combinations between another multiscale image transformation such as , , and other will be taken in addition to use alternative features reduction methods such as ICA, kernel PCA and other contemporary techniques are suggested to be used. In addition, the classifier type is suggested to change to show how the recognition accuracy could be improved. Although cancellable biometrics overcome the weakness of cryptography, current cancellable biometrics are still not secure enough for the palmprint identification. For example, attackers can still insert stolen templates replay and database attacks before systems can cancel the stolen templates and reissue new templates. Furthermore, current cancellable biometrics cannot detect replay and database attacks. In other words, if attackers insert unregistered templates into data links or databases, systems cannot discover the unregistered templates. To solve these problems, we can take advantages of cryptography and cancellable biometrics to design a set of security measures to prevent replay, brute force and database attacks for secure palmprint identification. One could improve the registration accuracy and the image combination process. A detailed study needs to be done on the effect of adding more frames for combination. This method could also be combined with the pose correction approach developed in the previous algorithm to make a robust system with further improved accuracy. In addition to these further directions, biometric researchers are in fact facing some open problems. Most biometric systems are examined only on zero effort attacks (general false acceptance rates). Do they still survive if experts attack them? Furthermore, how can we objectively evaluate and compare the security levels of biometric systems? It should be recognized that successfully breaking into biometric systems depends on money, time and knowledge. Biometric researchers are facing a dilemma. As we write everything to disclose our findings and algorithms for the sake of distributing knowledge to our society and the next generation, we are also providing the information that potential attackers require breaking into our systems.   Ãƒâ€šÃ‚  Ãƒâ€šÃ‚  Ãƒâ€šÃ‚  Ãƒâ€šÃ‚  Ãƒâ€šÃ‚  Ãƒâ€šÃ‚  Ãƒâ€šÃ‚      (b) Fig. 6.1 (a) A fake palmprint and (b) the corresponding genuine palmprint.

Leadership Interview and Analysis Essay

I interviewed the owner of a mid-sized engineering firm from this point forward referred to as Jack. Jack has been in the engineering field over 30 years starting as a project engineer and has worked his way to owning his own company. He has no formal training or degree in management or leadership and is speaking from experience. For Jack the definition of leadership is to guide and direct. He compares a manager in business to a platoon leader who can lead a group of people in a productive manor to achieve a desired outcome. When guiding these employees or soldiers the use of direct consequence or praise is the best way to guide your followers to the desired goal. Jack believes that most employees need close watch and a tight leash as to not fall off task. When Jack was asked what characterizes a good leader he continued to refer to the military example, even though he has never served. He believes there are two main components of a strong leader, wisdom and people skills. With wisdo m you will have a strong knowledge of the tasks or products offered and are able to assist in problem solving. Along with wisdom Jack believes that you will be able to make informed decisions and stay ahead of the market. People skills are the second part of Jacks components for a strong leader. When a leader has strong people skills he can relay his wisdom in an effective manner to employees so they can complete the desired task. He also believes that strong problem solving skills come along with people skills; you should be able to mediate an issue between employees or a client in a way as to not effect production or lose a client. Jack believes that situation plays a role in leadership. This is what separates strong leaders from the average. A strong leader can be placed in most any situation and be successful. If a mediocre leader is put into a simple or familiar situation they could be interpreted as a strong leader but will fail when tested. He also states that there are a few situations where even the strongest most experienced leaders will fail. The example of a pilot, seconds from destruction, could direct and organize his crew to the best of anyone’s ability and yet still fatally crash. This relates to business during market downturns and changes in technology. If you have too much expense and debt during a downturn or your only product has just been rendered obsolete by a new technology, there is not much you can do. When asked about the followers he prefers to refer to them as â€Å"the team† and they need to work together if they are going to be lead well. Although when asked if a strong leader can take â€Å"bad† followers and still accomplish a common goal, he believes it can be done. Jack still refers back to the military, when grunts come in general infantry they are generally â€Å"bad† followers but a strong leader can bring them together, have them work as a group and agree to go to war together. In Jack’s career he has encountered good and bad followers, some needing a lot of structure and others which could be trusted to complete the work with minimal supervision. Jack has a very â€Å"laid back† style of leadership and with some employees this became an issue because they took advantage of the freedom. In Jacks experience leaders can be trained but there is a small group that will never be a good leader. In society he believes there is a very large â€Å"middle ground† of people who can be trained to accomplish anything they set their mind to. He thinks that some great leaders are born that way and it comes much more effortlessly than for others. That being said, if one of the â€Å"middle ground† individuals had the desire and training they too can rise to be a great leader and accomplish great things. In general Jack believes that great leaders can either be born or trained to achieve the highest level of leadership and that there is a small g roup of individuals that un-salvageable. After this interview I think Jack has a understanding of what makes a leader but still has leaning to do. First and foremost leadership is a process and not just a single tactic to achieve a single goal. It is the development of relationships between the leader and the followers along with the relationships between the followers themselves. Through these emotional connections a leader can work with a group of followers and accomplish great things even when situation may be very difficult. I found it very interesting when talking about the characteristics of a strong leader Jack’s first response is wisdom, which I believe he relates to intelligence. Intelligence is a very large factor in being a strong leader but being inspiring is just as important. Being a â€Å"people person† does not make you a good leader. An individual can be very kind and a good listener but unless they can inspire a group of people to work together for a common goal they will not be effective. Jack believes that leaders can be trained to accomplish a high level of success much like the ones that are natural leaders. This is idea is in line with academics that leadership can be classically trained and not only gained by experience. Another issue with Jacks interpretation of leadership is how a strong leader can improve an already good situation. He sees that strong leaders can handle most situations and accomplish necessary tasks but fails to acknowledge that the entire dynamic is related. His views seem negative towards a leader with a good group of followers and a positive situation, that with a strong or marginal leader you will have the same result. I disagree with this idea and believe with a strong leader you can have increased productivity and quality of product. It also seems that Jack thinks all managers are leaders which is not the case. Managers and leaders have many of the same characteristics but hold different roles within a company. Managers are there to provide guidance and accomplish a short term goal or task whereas a leader is there to inspire and create a challenging vision for the long term success of a company. True leaders will be introspective as they learn from experience. This is known as the action-observation-reflection model in which a leader will take an experience and give it additional attention to learn as much as possible. First you must review the action that caused the experience, then review the outcome of that action and finally determine how you feel about the outcome. When using this method reviewing a situation one can gain a great deal of knowledge to apply in the future. Jack also seems to have fundamental attribution error when reflecting on why he considers an employee to be bad. He has a bias that when an employee is not functioning at their full capacity it is only due to them taking advantage of him and his method of management. He fails to see if there could be any outside factors causing these behaviors; for example, if an employee is also a student who in enrolled in a very difficult course may appear to be leaving early and â€Å"taking advantage† when in fact they just have a class to attend. This could be easily remedied by offering a flexible schedule where the employee could begin their work day a little earlier. This also relates to the self serving bias where this employee could hold Jack responsible for not performing in class instead of realizing they didn’t dedicate enough time out of class for study. Jack also believes that to be a good leader you must be very proficient in the task at hand. The academics disagree with this idea and note that the higher level of management the less technical knowledge you must have. This is where vision and inspiration become extremely important to guide your followers to success. In conclusion Jack has learned well from his years of experience but there is still room for growth in his knowledge of leadership and management, especially the difference between the two. Something that would greatly help improve the quality of management and leadership within the company would be using some assessment the leaders. This could be accomplished by having a questionnaire rating the leader by the superiors and subordinates. This method would help understand the performance of the leader as assessed by the superior and the effectiveness as provided by the subordinate’s questionnaire.

Characteristics of Poor Teachers

One would hope that all teachers would strive to be excellent, effective educators. However, education is just like any other profession. There are those who work extremely hard at their craft getting better on a daily basis and there are those that are just simply there never striving to improve. Even though this type of teacher is in the minority, just a handful of truly bad teachers can hurt the profession.   What qualities can deem a teacher ineffective or bad? There are many different factors  that can derail a teacher’s career. Here we discuss some of the most prevalent qualities of poor teachers.   Lack of Classroom Management A lack of classroom management is probably the single biggest downfall of a bad teacher. This issue can be the demise of any teacher no matter their intentions. If a teacher cannot control their students, they will not be able to teach them effectively. Being a good classroom manager starts on day one by incorporating simple procedures and expectations and then following through on predetermined consequences when those procedures and expectations are compromised.   Lack of Content Knowledge Most states require teachers to pass a comprehensive series of assessments to obtain certification within a specific subject area. With this requirement, you would think that all teachers would be proficient enough to teach the subject area(s) they were hired to teach. Unfortunately, there are some teachers who  do not know the content well enough to teach it. This is an area that could be overcome through preparation. All teachers should thoroughly prepare for any lesson  before they teach it to make sure they understand what they are going to be teaching. Teachers will lose credibility with their students quickly  if they do not know what they are teaching, thus making them ineffective. Lack of Organizational Skills Effective teachers must be organized. Teachers who lack organizational skills will be overwhelmed and, as a result, ineffective. Teachers who recognize a weakness in organization should seek help in improving in that area. Organizational skills can be improved with some good direction and advice. Lack of Professionalism Professionalism encompasses many different areas of teaching. A lack of professionalism can quickly result in a teacher’s dismissal. Ineffective teachers are often tardy or absent. They may fail to follow a districts dress code or use inappropriate language in their classroom.   Poor Judgment Too many good teachers have lost their careers due to a moment of poor judgment. Common sense goes a long way in protecting yourself from these sorts of scenarios. A good teacher will think before acting, even in moments where emotions or stressors are running high.   Poor People Skills Good communication  is essential in the teaching profession. An ineffective teacher communicates poorly, or not at all, with students, parents, other teachers, staff members, and administrators. They leave parents out of the loop about what is happening in the classroom.   Lack of Commitment   There are some teachers who simply lack motivation. They spend the minimum  amount of time necessary to do their  job never arriving early or staying late. They do not challenge their students, ​are often behind on grading, show videos often, and give â€Å"free† days on a regular basis. There is no creativity in their teaching, and they typically make no connections with other faculty or staff members. There is no such thing as a perfect teacher. It is in the nature of the profession to continuously improve in all areas, including classroom management, teaching style, communication, and subject area knowledge. What matters most is a commitment to improvement. If a teacher lacks this commitment, they may not be suited for the profession.

The Assistant Principal Darin - 1160 Words

It is just like any other day for Cathy Hurley, principal of Wylie E. Groves High School. She sat at her desk, blindly clicking through several emails, her tortoise glasses resting lazily on the tip of her nose. The sun was hidden behind several thick, grey clouds; it looked like it would snow later. The thought of getting new tires for the upcoming weather briefly crossed her mind when there was a sudden knock at the door, making her jump. She briefly fixed her glasses and smoothed down her hair before calling â€Å"Come in!† The assistant principal Darin Wilcox, a stocky babyish man, poked his head in. â€Å"Cathy, there’s an old man here to see you. He doesn’t seem to be the parent of any student or teacher here, though.†Ã¢â‚¬ ¦show more content†¦Ã¢â‚¬Å"Well, Mr. ‘Socrates’, how can I help you?† â€Å"All my life, I’ve pondered questions never expecting an answer. If I propose a problem or question to someone, they can ne ver seem to get it just right. Many will leave in a fit of rage, perplexed that I answer my own questions with more that seem to have no answer. However, in this room with you, in this school, I feel that it’s my duty to demand an answer for the problem I’ve come here for today.† Cathy sat for a moment in stunned silence. ‘Boy was this guy playing it up! Who does he think he is? Maybe he actually believes he’s the real Socrates!’ She thought. â€Å"And just what exactly is your question, sir?† Socrates gave her a look as fierce as a hawk would give its prey. â€Å"I don’t understand why you let hatred, bigotry, discrimination run through your school, infecting not only staff but students as well, like the vile disease it is.† This time, a wave of horror and confusion spread across her face. â€Å"I-I beg your pardon?! I have never heard of such things before, not from students, staff, anyone! I did not decide to run this school, just to make it a place where students feel unhappy! Kids love the environment here and are constantly making new friends.† â€Å"I have monitored this school for a long, long time Cathy Hurley. I have seen your proudly cherished students slam others against

Collapse Of The Mayan Civilization - 1024 Words

Patricia Licea-Chavez 10/27/14 History 2 Collapse of the Mayan Civilization There were multiple reasons for the collapse of the Mayan civilization. Some of these reasons are environmental damages/overpopulation, natural disasters, and warfare.(The) Out of these the most likely reason for their collapse was war. (Cartwright) Within this war there were also the battles that were going on within its civilization, the offerings that they made to their gods, and the campaigns to resist the Spanish conquest. In the beginning the Mayans were thought to be a very peaceful civilization. It was also a rare occasion when they got into an altercation with another tribe. But recently historical anthropologists have discovered new meanings to the inscriptions on the stonework on the Mayan site of Dos Pilas. These new finds have told us that the Mayans were very violent people. The Mayans thought that war was very important because it gave them prestige when they took over neighboring city-states and captured prisoners to either enslave or make them sacrifices. One of the rituals the Mayas had was to give offerings to their gods. They would fight amongst themselves, while Venus was in sight. Venus was supposed to bring signs of destruction and mess up the government. The Mayans would also sacrifice themselves by playing a game, the ball game. This spiritual game was played with decapitated heads used as the ball. The game was also a â€Å"sequel† to triumphant battle. The enslaved soldiersShow MoreRelatedWhy Did the Mayan Civilization Collapse?2267 Words   |  10 PagesTo gaze upon the majestic ruins of the Mayan civilisation which collapsed over a thousand years ago, one is often stirred with wonder and a deep sense of curiosity (Diamond, 2005, p157-8). What happened to this great empire and what brought about its demise? The tremendous task of erecting such elaborate and colossal structures was clearly performed by the hands of a well-organized and adept group of humans (Crist and Paganini, 1980, pg24). Their empire occupied a vast area of roughly 325000 squareRead MoreEssay on Did the Mayan Civilization Collapse as a Result of Drought?1016 Words   |  5 PagesEver since the collapse of the once powerful Maya civilization, people have been trying to find out what caused it. Authors of the article, “Climate and the Collapse of Maya Civilization”, which include Gerald Haug, Detlef Gà ¼nther, Larry Peterson, Daniel Sigman, Konrad Hughen, and Beat Aeschlimann propose a theory that the Mayans collapsed because of an extended dry period between 760 and 910 A.D. These scientists set out find the answer as to why the Maya civilization collapsed. ThisRead MoreIs The Classic Mayan Civilization?1558 Words   |  7 Pagesof Anthropology, a collapse is defined as â€Å"†¦a drastic decrease in human population size and/or political/economical/social complexity, over a considerable area, for an extended time.†(AOC) With Mr. Tainter’s definition of collapse, I will be focusing on one specific civilization, what led to their falling as a society and elaborate on some theories as to why collapses may occur. The development that I am going to be discussing is the Classic Mayan civilization. The civilization was located in MexicoRead MoreEnd of Mayan Civilization1143 Words   |  5 PagesEnd of Mayan Civilization Samuel Nathaniel H. Stansbury HUM 111 11/3/2012 The mystery concerning the fundamental explanation for the collapse of the Mayan Civilization has been a major focus for researchers in the fields of anthropology and archeology for a considerable period of time. At the very core of this mystery of the Mayan collapse was the question of how could such a strong, stable civilization that had flourished for approximately twenty-seven hundred years disappear without a clearRead MoreMaya Civilization Collapse1311 Words   |  6 PagesThe example of societal collapse in which I will be making reference to throughout this essay is the Maya civilization. The Maya civilization is, â€Å"probably the best known of all early American civilizations.† (Fagan, 1995) It was at its strongest point between AD 300 AND 900. Around AD 900 was the time of its collapse. This civilization was developed in a densely, tropical forest on either highlands or lowlands. Today to visit a Mayan site, people would go to the modern Mexican state, capital ci tyRead MoreThe Fall of the Mayan Empire Essay1517 Words   |  7 Pages The fall of the Mayan Empire The collapse of the Mayan Empire is one of history’s greatest mysteries. It was one of the most advanced and developed civilizations of its time period, reining during the Pre-Classic period and into the Classic and Post-Classic Periods (2000 B.C. – 900 A.D.). The territory stretched from the Yucatan Peninsula in Mexico, down to modern day El Salvador in Central America. Its achievements were monumental for the era, being the first empire communicating with the useRead MoreCollapse of Civilizations1323 Words   |  6 Pagesfactors that lead to the collapse of civilizations are almost directly related to those that created it. Archaeologists characterize collapse by a number of elements, some of which we have evidence for, others we do not. Most archaeologists are unsure of exactly what caused the decline of most civilizations in the ancient world, yet there are many clues to some of the events that could have contributed. The collapse of the ancient Roman Empire, the Mesoamerican Mayan, and the Egyptian culturesRead MoreThe Ancient Civilization1622 Words   |  7 PagesThe intrigue of The Mayans has always existed through the telling of their ritualistic practices or their calendar, but the fall of such an advanced civilization is perhaps the most intriguing story of all.To understand what causes great civilizations, it is vital to note the process of collapse in other civilizations, such as the great Roman Empire. Differences in time period, geographical landscapes, and other circumstances mean no direct correlations are possible, but the outstanding point ofRead MoreEssay The Maya Civilization904 Words   |  4 PagesMaya Civilization The ancient Maya once occupied a vast geographic area in Central America. Their civilization inhabited an area that encompasses Mexicos Yucatan peninsula and parts of the states of Chiapas and Tabasco, as well as Guatemala, Belize, Honduras, and El Salvador. From the third to the ninth century, Maya civilization produced awe-inspiring temples and pyramids, highly accurate calendars, mathematics and hieroglyphics, and a complex social and political order (Collapse...Read More Collapse of Civilizations Essay1292 Words   |  6 Pagesfactors that lead to the â€Å"collapse† of civilizations are almost directly related to those that created it. Archaeologists characterize collapse by a number of elements, some of which we have evidence for, others we do not. Most archaeologists are unsure of exactly what caused the decline of most civilizations in the ancient world, yet there are many clues to some of the events that could have contributed. The collapse of the ancient Roman Em pire, the Mesoamerican Mayan, and the Egyptian cultures